Bug 1813987: resizing wall/gallery block when content change

wall
- resize the block when adding a new post
- resize the block when the tinymce is changed
(menu expanded/textarea resized)

image gallery
- resize the block when the block has a slide show
and the image is changed

behatnotneeded

Change-Id: I7fe0624285443b6173d9bd5f5be488539f6da03d