add support for importing from Google Docs

[bnwest]

New entry in the Add drop down: New Google Doc Import

When that entry is clicked:

1. Google Doc picker is thrown
2. Html for selected Google Doc is fetched for google
3. Called remix's gdoc2html service which transform html into aloha-ready html
4. aloha-ready html is put into the editable area

Unresolved issues:

• Icon for New Google Doc Import is Google+ and not Google
• Using gdoc2html from http://testing.oerpub.org/ instead of http://remix.oerpub.org/ (just need to release remix)
• If the GDoc import fails (or user cancels out of the picker dialog box), we need to run some cleanup code. release does include an empty stub _cleanupFailedImport() that needs to be filled.

[bnwest]

remix.oerpub.org has issues (kef -- "gh-book stuff broke being able to drag semantic elements in remix") and can not be released at this time, so we are stuck using the gdoc2html service on testing.oerpub.org for now.

[philschatz]

🍰 !

[izak]

I'm closing this, it's been superseded by #75.