volume viewer: improve behavior of non HDF5 files
When the volume viewer tries to display something else than HDF5 it requires to load everything in memory. This could bring to freezing gui as this is done in the main thread.
To avoid this we could:
- do this asynchronously. But when a new volume arrives it should be handled
- create a master .hdf5 files for tiff, edf... providing on the fly loading of the volume. ( Might be tricky for chuncks and performances as well)