Extend type checking for container templates. Add utility
function to obtain container size.

Put it in new top-level "Maemo" category, along
with the Maemo device configurations.

Reviewed-by: kh1

Add a tooltip for disabled toolchains in the selector dialog.

Delay the setup of the UI until the Debug mode is activated. This is
required by the Debugger now setting up most of it's UI in
extensionsInitialized ...

Don't mark plugin as experimental. Probably got introduced by some
merge.