This was added a few years ago, as a way to have _no_ im context
at all. But it didn't actually work. Make it work, and streamline
the handling of none by moving it all to gtkimmodule.c.
As part of this, add context to the translated names of all
im modules we ship.
We add a custom im module for broadway that calls some broadway
specific APIs to show/hide the keyboard on focus in/out. We then forward this
to the browser, and on the ipad we focus an input field to activate
the keyboard.