VoxelEditPacketSender class improvements

- better support for non-threaded usage
- now process() will not sleep in non-threaded mode
- now process() will determine number of packets to send per call based on average time of calling
- added support for hinting to how often the caller will call process()
- changed name of flushQueue() to be more clear
- added support for buffering up pending edit changes if no voxel servers are present.
- changed assignment client, interface, and animation server to support new API
- added "non-threaded" support to animation server