Previously drafts called compose.snapshot_message which would then
get the message object from compose.create_message_object. This method often
checked for the validity of stream/user recipients which would often cause tracebacks.
The new method in drafts.snapshot message just gets the data from the fields and
stores them in the draft model without any additional checking.
The addDraft and editDraft tests were copying objects by reference
which meant the methods weren't tested properly. Due to this, a bug with
stubTimestamp was also discovered where the method wasn't getting stubbed
* Created a drafts modal to display/restore/delete drafts
* Created a Draft model to support storing draft data in localstorage
* Removed existing restore-draft functionality
* Added casper and node tests for drafts functionality
Fixes#1717.
