VOXELFORMAT: refactored interface to work with archives and not on st…

[mgerhardy]

…reams

this allows us to support multi file formats in a better way

Fixes issue #460

• [x] Segfaults
• [x] Performance
• [x] CubzhB64Format.cpp doesn't search the cache dir anymore
• [x] Use raw pointers and use a Dispose flag