Rather than enumerating available classes, define an event that sets a
flag indicating that there's an IM plugin available. Implemented in
implugin.php, so all IM plugins that use that class should
work. Others can hook the event, too.
There's a new menu layout in this version of the software. It was
implemented as a plugin in 0.9.x to avoid clashes with existing themes,
but we're going to break that compatibility in this version, so we're just going for it.
This change involved moving all the changes in NewMenuPlugin into the
default code that was calling it. In addition, since
accountsettingsaction and connectsettingsaction differed only by menu,
I removed them, changed all references to them to the settingsmenu, and moved
the combined nav to its own class.
Let's put that episode behind us.
The CSS shim that was loaded by NewMenuPlugin for certain themes and certain actions
was removed.
