Line mesh rendering

See merge request iMSTK/iMSTK!232

ENH: implemented a clearing function for line mesh and improved description for setting the color of a material

Download unit test data separately

See merge request iMSTK/iMSTK!252

Separate sandbox examples into stand-alone projects

See merge request iMSTK/iMSTK!251

1 or 2 line descriptions are added for each example.

Remove shader compilation code from audio example
remove PBDFluid benchmarking example

COMP: Update the Eigen remote repo link

See merge request iMSTK/iMSTK!249

COMP: rename output debug lib for gmock/gtest

See merge request iMSTK/iMSTK!248

COMP: Update Google Test to fix compilation on msvc 15 2017

See merge request iMSTK/iMSTK!247

Addresses following issue:
https://github.com/google/googletest/issues/1373

Add multiple sources for Libusb download

See merge request iMSTK/iMSTK!245

Sometimes the sourceforge server appears to be down, stopping us from
downloading libusb1.0. We now add a second url to fetch the libusb
package from data.kitware.com

To include following feature:
cmake/cmake@2eec433f

Fix ubuntu

See merge request iMSTK/iMSTK!246

https://github.com/assimp/assimp/issues/746
https://stackoverflow.com/questions/38296756/what-is-the-idiomatic-way-in-cmake-to-add-the-fpic-compiler-option