Extensions that use public Shell API are expected to work for all
stable 3.0 releases, so we skip setting the minor version. (This
means that they'll work in 3.0.0 and 3.0.1 without rebuilding).
Notably absent are auto-move-windows and windowsNavigator, that
hook deep into Shell code and could be broken by next minor release.
GNOME Shell emits a warning when "url" is absent in metadata.json,
adding it costs nothing. Links to the GIT repository because I
found no better page to reference.
Fix the behavior of the PopupMenu after the conversion of
St.Clickable to St.Button, and fix the invocation of ShellApp.open_new_window(),
which now accepts a workspace index as a number (as a side effect,
"New window" means one the current workspace now).
