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.
* 'd' in message view opens drafts.
This also adds hotkeys within the drafts UI:
* Up/down arrow keys navigate the drafts.
* Pressing enter edits the selected draft.
* Pressing backspace deletes the selected draft.
Some variable names tweaked by tabbott.
This consolidates all actions to close modals into modals.js and
triggers the correct cleaning/collapsing function dependent on what the
data-overlay attribute is labeled as.
It also ensures these all have an e.stopPropagation().
Fixes#4029.
* 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.
