Fix carousel tile so it does not break cover when dropping content with no image field (fixes #371)

- Remove galleria-inner CSS class form tile template and styles
- Add upgrade step to cook CSS resources

As a side efect, carousel tile is now fully responsive and image size used will match the one configured for the tile.
Update changelog
Merge pull request #404 from collective/issue_371

Fix carousel tile so it does not break cover when dropping content with no image field