Removed Entity::qPitch/Yaw/Roll

These were protected, and grep revealed they were not used anywhere.
Converted Entity::tags to a pointer.

The idea is that most entities don't use tags, so wasting space on it when it's not needed isn't a good idea. tags is protected, so this does not affect the public API. All the functions that use tags were updated appropriately.
Merge pull request #265 from CIB/less-memory

Entity memory optimizations