The most common thing that we do with fab! is:
fab!(:thing) { Fabricate(:thing) }
This commit adds a shorthand for this which is just simply:
fab!(:thing)
i.e. If you omit the block, then, by default, you'll get a `Fabricate`d object using the fabricator of the same name.
This patch adds a new shortcut to allow archiving private messages. When
on a private message page, just type `a` to archive it. Typing `a` on an
already archived message will move it back to inbox.