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To make sure we always use the correct device adapter force only
a single device adapter to be on.

Also
- Renamed vtkm::cont::make_DeviceAdapterIdFromName to just overload
  make_DeviceAdapterId.
- Refactored CMake logic for unit tests
  - Since we're now querying the device tracker for the names, they
    cannot be all caps.
- Updated usages of InitLogging to use Initialize instead.
- Added changelog.

Addresses #291.

Rather than force all dispatchers to be templated on a device adapter,
instead use a TryExecute internally within the invoke to select a device
adapter.

Because this removes the need to declare a device when invoking a
worklet, this commit also removes the need to declare a device in
several other areas of the code.