improve how Joomla menu items are built

there are several improvements we should make to how menu items are built in Joomla. specifically:

• the asset being selected (event, profile, contrib page, etc.) should be a required field. if a menu item is built without selecting an option it leads to an error (for obvious reasons).

• move the asset selection to the main configuration tab. currently it's in a second "Options" tab, which is easily overlooked. since in each case it's only one field we're working with, we should just include it on the main tab.

doing so will also change how the values are passed to civicrm for invoking. currently we retrieve the params for the menu item. by placing them on the main config tab they become part of the $_REQUEST variable, and so we must retrieve them differently.