Added Evernote App Integration

Requires the Evernote Android App!
Creates an anki note for every evernote note matching the Evernote search string specified in the preferences. Doesn't synchronize contents but only the Evernote note ID. While reviewing the anki notes the associated Evernote note will be opened in the Evernote App. Tap the return key to get back to AnkiDroid and rate the difficulty.

!!! VERY EARLY STATE !!!

2nd try: now only one commit (rebase didn't work, so I created a new fork and made all the changes again)