Use the mobile.startup module mfExtend export directly instead of
OO. This will allow MobileFrontend to reduce its exposed API.
Bug: T208915
Depends-On: Idededf132f724176c38c5e0a7c9327f00489a09d
Change-Id: Id582325c830c229240b88cf4e151afea48fea750
This experiments with making PageIssuesOverlay an Overlay with
various options.
The appending of children is a little messy and points at a need
to standardise this some way
(see https://phabricator.wikimedia.org/T209647)
TODO:
* Remove the iconString property on PageIssueSummary which is no longer
needed
Bug: T209647
Change-Id: Iadd798a820dca6bbb31edc9a8570b6db7aac237a