Added a popularity filter that allows to filter out caches that have more  then a predefined number of favorite points

Sorry - I messed up the first pull request by using the wrong browser. Here is the same again:

The filter allows to filter caches with more than 10,20,50,100,200, and 500 favorite points.

BTW: I would recommend to rename the German translation of Popularity from "Beliebtheit" to "Favoriten" since this makes the filters and sorts much more intuitive to use for a German cacher. I have not changed anything because I guess that such an HMI change would require a formal request in some forum. So my ask is: where can I request it?
If it is approved I would set up a new pull request for the name change.

As for the tts_ string naming: I took it from another similar filter, the DistanceFilter, assuming that this is the reference implementation for a filter.