Suppressed warnings
Some cleanups in the DICOM importer, and fix importing some sequences

Some DICOM sequences had each slice with an independent Series Instance
UID, thus confusing the importer which would import each slice as a
separate volume. Now we rely on Series Description, hopefully more
reliable. I also removed the Series Number from the volume signature.
Change computation of bounds for window/level (handle negative values)
Change composite param to use QHash to set values (was buggy before)
Remove useless qdebugs
Solves the problem of window level using the sliders with images having small value ranges
Window limited to 0 everywhere
Correct number of decimals shown based on current step
Correct WL transmission bug between 3d and 2d view
Added some comments to justify the use of (void), and cleaned-up some commented code
Merging fcollot:remove-warning, closes PR #148
Correct zooming bug in 3d mode
Levels are not constrained by image values anymore
Merge pull request #157 from ocommowi/wl-composite-bug-correction

WL composite bug correction
Correct some stuff in ROI loading, still buggy
ROI manager is hard coded for unsigned char images, convert input
Remove useless labels from ROI list
Compute local and global orientations when reading fibers if they weren't there
Color modes list updated automatically
Correct errors in fiber stats computation