UPnP - add different groupings for content in video

Video section in UPnP lack any sub-classification like in Recordings section. This makes it very hard to orient as soon as the user has more than a few videos. When I started to use MythTV as DLNA server,
this is what I lacked the most. Surprisingly it is extremely simple to add new grouping. The code is practically prepared for that, since the beginning. I  would be very happy to add this feature with my patch.

This patch adds eleven new groupings. these are :
- by folder (that is, by last directory name in which is the file located. i.e. not the full path)
- by length (rounded to nearest 10)
- by user rating (rounded to integer)
- by maturity rating (i.e. 12, 18, PG, etc.)
- by category
- by director
- by studio
- by homepage
- by year
- by content type
- by season

All these groupings are only 1 level groupings, but in my opinion quite useful. For example folder name in which the file resides is relatively useful classification. Grouping by length rounded to nearest divisible by 10 minutes usually groups together the same series, making them easy to find. Most of these groupings are based on videometadata table, which may be updated automatically or they may be filled manually with reasonable data.

I think even if somebody does not use all the groupings, it definitely does not harm to have it.