[PATCH] Add tags through a cell in the tags view instead of a dialog

[Eric Lesh]

This patch gets rid of the "New Tag" dialog and instead adds a "Type a
tag" entry at the bottom of the tags list for editing.  This is how
Epiphany works in the bookmarks editor when adding a topic.

You commented in the code that "For intelligent tags we'll need a dialog
here."  I'm not sure what you you meant by that, but I think the dialog
is a bit of a nuisance.

In case you didn't have other plans for the dialog and just forgot that
bit of code, here's a patch.

-Eric