Square thumbnails + manage gallery thumb sizes
VID-1854
Merge VID-1854-gallery-prototype, Conflicts:
extensions/wikia/MediaGallery/MediaGalleryController.class.php
extensions/wikia/MediaGallery/templates/MediaGalleryController_gallery.mustache
Move getDimensionMultiples to new gallery helper
per @lizlux
Fix missing thumbnail alt, default to file title
Fluid style class should be applied to both image & video
Exclude dimensions for fluid images
/CC @lizlux
Minor fixes per feedback
VID-1854 Refactor media gallery helper to allow all gallery sizes
/CC @lizlux
Update comment for DIMENSION_UNIT
Merge pull request #4426 from Wikia/VID-1854-square-thumbs

VID-1854 square thumbs