Cleanup code for mod_finder

Main thing of this PR is to make the `set_itemid` parameter so it uses the `menuitem` formfield instead of a `text` formfield. This lets users easily choose a menu item instead of looking up the id in the menu manager.

I did some other cleanups while working with he code:
- Change `show_autosuggest` from list to radio formfield and added classes so it shows as red/green buttons
- Moved the `alt_label` parameter below the `show_label` parameter as it makes more sense there
- Adjusted some default values to be in line with the default values in the code. If the are objections with this it can be easily changed. My only concern is to have them consistent in the XML file and in the code.
- Removed `JHtml::_('behavior.framework');`. We don't use Mootools anymore and JQuery is loaded together with the tooltips anyway. So no need to specifially load the framework.
- Cleaned up code related to the `switch` statements for `button_pos` and `label_pos`
- Removed an unneeded `if` for the `show_advanced` parameter

I think there should be no changes at all for existing sites.