Changes:
1. Javascript decoder can now be built separately for meshes and point
clouds. Together with other optimizations this results in about 33%
smaller Javascript for mesh decoder. (pre-built javascript for meshes
and point clouds is included).
2. Fixing bug in our symbol_encoder that resulted in failed encoding for
certain cases when there were around 1<<18 symbols.
3. Changing default setting of our draco_encoder app to -cl 7
1. Added support for loading sub-objects in .OBJ into a generic
attribute.
2. Added missing mesh_are_equivlent classes needed for certain unit
tests.
3. Updated javascript decoder reflecting our latest changes + added
support for GeometryAttribute::custom_id() method.
4. Added checks for valid quantization bits to our draco_encoder app.
