added dir selection

some changes, please review minutely. No, just kidding. Added the ability to navigate/filter based on dir selection. This needed some additional DB tables and design (Hierarchy).

Some starting errors (runtime errors) made me to make the db layer more restrict. So every DB query has now a PROJECTION and a TARGET. Projection is the scope you can filter (means use the in where query using SQL), target is the result (what can be mapped to an instance from the result). So my early errors using filters on not wide enougth projections gets now compile errors.

Known bug: Directories without mp3 inside but with mp3 files in sub dirs gets not catched. Need to change the logic there. FsReader:125

Hope i catched all the changes of reverted and reapplied change package commit.