BK-1288 Thumbnails for certain cover types or error thumbnail are broken

Inserted images to new position and corrected paths
BK-1185 Show user chat in the editor
Merge branch 'BK1185' into 2.0
Merge branch 'BK1288' into 2.0
Merge branch '2.0' of https://github.com/sourcefabric/Booktype into 2.0
BK-1289 Book metadata in the editing interface