Insertion arrow behavior update

This adds back the blue arrow to indicate where an image will be inserted.

Stuff that needs doing
- [x] Make multimedia embed arrow behave (not stick around when the action is canceled).
- [x] Unify arrow treatment. Make all (table, image, video) arrows the same arrow and color. I like the table color best (highlight blue). Lets try using an arrow from font awesome.  http://fortawesome.github.io/Font-Awesome/icon/arrow-down/ perhaps. 
- [ ] Fix error (or make new issue if it is just coincidence.) Remote updater: Upon opening http://33.33.33.10/#repo/oerpub9/new-book-92/edit/content/module1.html|content/mybook.opf, get "Remote updater running twice." (This doesn't happen on master for me.)