mw.ViewPageTarget.init: Move edit section to top init

Since we're now only loading the light-weight init on page load,
the section editing wasn't just deferred to after page load (like
it was before), but wasn't happening at all until you clicked
"Edit" (at which point the library loads). It only worked when
going back to "View" after "Edit".

Contrary to tab layout, edit section handling needs to be
accessible both in the top init and in the main target class
because we need to run it both at run time and after the user
has saved a page when we show them the updated page without
refresh. This is why we need to transfer the method at run time
and give the main class access to it as well.
Can't wait for bug 50707 to get rid of this mess...

Bug: 50731
Bug: 49993
Change-Id: Iab9c81222df7f1084179c3643d158374a89ca14b
Merge "mw.ViewPageTarget.init: Move edit section to top init"