Support SharedNoteBooks

[roblabla]

Heya, This is similar to issue #28, but in the context of shared notebooks. The idea is that notebooks shared between two users need to be accessed differently from personal notebooks. Here are the steps :

1. Call ListLinkedNotebooks, which will give you a list of LinkedNotebooks.
2. Create a new NoteStore with LinkedNotebook.shardId, and use authenticateToSharedNotebook against it.
3. Call getSharedNotebookByAuth with the resulting Authentication Token
4. Done, we now have our shared notebook, and may use it to retrieve notes.

Now, here's the problem : when saving a note retrieved from a SharedNotebook, we need to remember the URL of the shard we connected to, lest the server replies to us with an error (or worse).

I'll try comming up with a Pull Request once I manage to get this all working.

PS : I have to say, the evernote docs aren't very clear, and the API kind of stinks... Why would shared/linked/business notebooks get special treatment at the API-level is beyond me.

[bordaigorl]

@roblabla this is great! I could really do with some help on this... the API for shared and business notes is so cumbersome to use! I'll be glad to review your PR and help you improve the plugin. If you need help just ask!