Update metadata.xml

Add Subcategory Level parameter to Series menu to allow per menu setting as discussed @: http://www.sermonspeaker.net/forum/sermonspeaker-4-x-support/2616-category-options-per-menu-item.html
Add subcategory levels to Sermons
Add subcategory levels to Speakers
Merge pull request #13 from MDunkleSr/patch-1

Adding an option to the menu items which allows to set the subcategory levels.