Documentation revision
Revision based on comments.

1. Add documentation.

2. Move startCamera() and stopCamera() to DeviceData

3. Move setPositionScale() and setOrientationScale() to DeviceData

4. Add 'm_' to DeviceData's member data

5. Drop redundant 'result' in TrackIRScaffold::registerDevice()

6. Use SURGSIM_ASSERT() to only allow one TrackIR camera in the scaffold
TrackIRScaffold Linux driver revision

1. Remove unused headers.

2. Add 'm_' to DeviceData member data.

3. Drop redundant 'result' in TrackIRScaffold::registerDevice(),
   TrackIRScaffold::initializedSdk() and TrackIRScaffold::finalizeSdk().

4. Remove startCamera() and stopCamera() methods (they're unused).
Revise UnitTests