Test Angle class can be created and read

Also add AngleTest supporting code
Add initial Angle class
Test Angles can be created specifying degrees too
Add Angle methods to create by and get degrees
Test Angle objects can be compared
Add comparison operator
Separately test angle conversion and comparison
Test Angle copy constructor

The default C++ copy constructor is sufficient for now, so there's no
new code added, but this test is here just in case that someday needs to
change.
Test copy assignment operator

Again, no code needed currently.
Add Angle addition operator
Add Angle subtraction operator
Add Angle scalar multiplication operator
Add Angle scalar division operator
Add compound assignment operators
Convert scene graph generation to use Angle class
Convert RotationNode to use Angle class
Merge branch 'angleClass'