Streamlined task edit form.

The task edit form is now entirely inline, and makes use of several new
directives that encapsulate common autocomplete logic. Creation and
editing can now be controlled entirely from the keyboard, though clicking
'save' on a new task will not (yet) reshift focus to the new row.

- New user-typeahead directive.
- New project-typeahead directive.
- New 'editable' text directive.
- Tab enabled controls
- Focus directive can now be turned off.

Change-Id: I85657b9c61fcefcf13c01235e3c9b14b9268a65d