Add user plugin manager / download tool.
Not very well integrated nor pretty.
Still requires a restart, needs more hooks into config dialog. (Clean up
previous plugin vboxes after installation. Auto-activation required to
reimplement init loader. And channels.__path__ setup isn't yet injectable,
because no plugin `order:` is honored by main/init, and pluginmanager2
would run too late for overrides.)
check-in: 8e8a9dd020 user: mario tags: trunk