deployed v8a
answers options now in an external file for simplicity's sake
fixed stats sending also when there are no correct answers
started implementation complex exercise tree.

- added JSON answers dictionary: a "simple" (one-level answers list) and "complex" (multi-level answers tree, to be done)
- added an additional button for the teacher
added global switch in app.yaml to select local or CDN jquery path
added out-of-focus alert and fix student username bug.

- added student out of focus alert in teacher dashboard (console.log so far, to be tuned in front-end
- added a fullname attribute in the user object, to separate username (no blanks) and full name (with spaces)
- restore the automatic student name removing when disconnected, and connection alert on teacher dashboard when student close the browser
Merge pull request #53 from erpreciso/backend-dev

Backend dev