Bug 847168 - [User Story] Email Signature

You do not need to add this dependency here.  It's already available off of composer.mailchew inside _cmd_beginCompose.  By adding the dependency here statically, as can be seen in the gaia pull request, moving more JS code into our worker startup path which slows down worker startup.  In general you do want to try and keep an eye on the effect of the files/layers we install into gaia for these reasons.  (It can be a hassle, but it matters.)

Please feel free to add a comment here or around the use point or what not to help make this generally more obvious.

Or if you're feeling fancy, we could alternately split much of _cmd_beginCompose out to be its own module which can then have static dependencies and itself just be a dynamic dependency, etc.  I'm okay either way although in the long term we all know we need to make mailbridge.js much smaller.