missing colour background in Media Overlays UI
disabled pan-zoom (as the feature is currently broken), and removed text annotation tool too (was already disabled in Chrome extension)
Added back zoom interface for testing
Update sub-module & readium.
Update sub-module & readium.
fixed list view image thumbnails being resized as if they were in grid view, regression from #71
Merge remote-tracking branch 'origin/develop' into feature/mathjax

Conflicts:
	readium-js