Made dataBuffer be common for all holograms. Also thoughts about hologram memory usage.

The reason was that my client crashed because garbage collector wasn't able to free 486 MiB for all these dataBuffers for 36 holograms I was looking at (still alive @4FPS on my Intel HD 4600 by the way)

However, the main problem I didn't quite think before is the fact that **holograms consume tons of video memory**. Common 'skeleton' uses *47.25 MiB* and each hologram (*even empty!*) eats up *extra 13.5 MiB* of video memory. Although GPU is usually able to use part of system RAM when no free video memory remains, it has huge performance penalty and discrete GPUs are usually limited to 2 or 4 GiB total.