Removes obsolete setting of CMAKE_GENERATOR_* variables in imstk_add_external_project,
indeed these variables are now automatically passed to projects from within
the updated imstkSolveDependencies CMake module.

This commit updates the build system to follow the established CMake
convention.

It also allows the use of iMSTK custom find package in the context of
external project named after the library being integrated and avoid
target name conflicts.

References:

* Double colon in target name means ALIAS or IMPORTED target.

  Source: https://cmake.org/cmake/help/latest/policy/CMP0028.html

* This convention of double-colons gives CMake a hint that the name
  is an IMPORTED target when it is used by downstreams with the
  target_link_libraries() command. This way, CMake can issue a
  diagnostic if the package providing it has not yet been found.

  Source: https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html

Similarly to the pair <package>_ROOT_DIR/<package>_LIB_DIR used by
"imstk_find_libary", this commit support specifying a custom include
subdirectory associated with "imstk_find_header".

This commit removes the requirement for systematically passing <package>_LIB_DIR
in addition of <package>_ROOT_DIR by setting <package>_LIB_DIR to "lib" if not
already defined.

This commit ensures library like "libusb" can be found on linux
by updating the list of accepted library suffix.

This commit ensures the custom find module can be used to set the
variable "<package>_INCLUDE_DIR" in the cache similarly to how the
"<package>_LIBRARY_<library>-<config>" are set.

This is particularly useful when integrating iMSTK in other packages
where the packages may have to be looked up prior configuring iMSTK.

This commit streamlines maintenance by ensuring the variable set by the
iMSTK custom find package modules are named after the package being
discovered.

It fixes warnings like the following:

```
  CMake Warning (dev) at /path/to/cmake-3.20.1-linux-x86_64/share/cmake-3.20/Modules/FindPackageHandleStandardArgs.cmake:438 (message):
    The package name passed to `find_package_handle_standard_args` (LIBUSB)
    does not match the name of the calling package (Libusb).  This can lead to
    problems in calling code that expects `find_package` result variables
    (e.g., `_FOUND`) to follow a certain pattern.
```

This commit ensures custom CMake/FindXXX.cmake package specifying that
the debug library should be the same as the release library are effectively
looking up the expect library to set the variable `${PACKAGE}_LIBRARY_${library}-DEBUG`.

Without this commit, running cmake specifying `--debug-find` argument
at configuration time incorrectly included USE_SYSTEM in the name of the
debug library to lookup.

For example, here is the output associated with Libusb reported on Linux:

```
$ cmake --debug-find .

[...]
  CMake Debug Log at /path/to/imstkFind.cmake:148 (find_library):
    find_library called with the following settings:

      VAR: Libusb_LIBRARY_libusb-1.0-DEBUG
      NAMES: "libusb-1.0USE_SYSTEM"
             "liblibusb-1.0USE_SYSTEM"
      Documentation: Path to a library.
      Framework
        Only Search Frameworks: 0
        Search Frameworks Last: 0
        Search Frameworks First: 0
      AppBundle
        Only Search AppBundle: 0
        Search AppBundle Last: 0
        Search AppBundle First: 0
      CMAKE_FIND_USE_CMAKE_PATH: 1
      CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH: 1
      CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH: 1
      CMAKE_FIND_USE_CMAKE_SYSTEM_PATH: 1

    find_library considered the following locations:

      [...]
      /usr/local/sbin/(lib)libusb-1.0USE_SYSTEM(\.so|\.a)
      /usr/local/bin/(lib)libusb-1.0USE_SYSTEM(\.so|\.a)
      [...]

    The item was not found.

[...]
```

REFAC: Fix warning, Remove CollisionConstraint Enum

See merge request iMSTK/iMSTK!746

BUG: Fix enableBendConstraint for multi strided bend constraints & fix stride iteration

See merge request iMSTK/iMSTK!743

BUG: Add collision re-enabled

See merge request iMSTK/iMSTK!744

ENH: Toggle for vsync

See merge request iMSTK/iMSTK!742

REFAC: Interactions now SceneObjects

See merge request iMSTK/iMSTK!733

REFAC: Update RigidObjectLevelSetCollision for interaction refactor, RigidObjectCollision measureDisplacements node addition

ENH: Update C++ to 14

See merge request iMSTK/iMSTK!738

REFAC: Warning for multiple meshes when assimp reader is used

See merge request iMSTK/iMSTK!736