We need to use it in more than just the context of mobile, and
there is nothing actually mobile-specific in it. Renaming the
class so it isn't awkward to use elsewhere.
This makes the ext.echo.ui.mobile module unnecessary, but
we leave it in until next patchset so that MobileFrontend
doesn't crash while we wait for the adjustments in
Ie592ca738ac2d8 to be merged.
Change-Id: I7891eb3fb46b350f0b325bf0a2b56b2cd55ff1d7
