breakup-984365: Make the 'command' item type the default

So now you don't need to say item:'command' in each command.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
breakup-984365: Update [add|remove]ItemsByModule to take options

This allows us to specify delayed loading properly.

Signed-off-by: Joe Walker <jwalker@mozilla.com>