Added camera data to AvatarData class, and include it in interface
Made several ViewFrustum methods const since they don't modify the class
Derive VoxelAgentData from AvatarData to get access to camera details
- Changed base class for VoxelAgentData
- changed parseData() method to call base class implementation
- added avatars library to cmake scripts
First cut at View Frustum Culling between client and server
Merge branch 'master' of https://github.com/worklist/hifi into view_frustum_work

Conflicts:
	voxel-server/CMakeLists.txt
code review cleanup
code review cleanup
code review cleanup
code review cleanup
code review cleanup
change VoxelAgentData to not include position, use AvatarData _bodyPosition instead
Merge pull request #102 from ZappoMan/view_frustum_work

First Cut at View Frustum Culling between server and client