feat(graphics): synchronize 2D negatos when picking
* Synchronize 2D negatos when cliking on the image. * Add a parameter in `SVoxelPicker` to enable the update of image slices indexes. Send `::fwData::Image::s_SLICE_INDEX_MODIFIED_SIG` with the picked indexes. Closes #666 Merge branch '666-graphics-synchronize-2d-negatos-when-picking' into 'dev' See merge request !540