Humanreadable search

This is based on the #186. I refactored the parsing of the time input to use QRegexp directly and added a special query node for the time-querys because they are now not purely numeric anymore. 

To search for a track of exactly 90 seconds the following terms are equivalent.

90
90s
1m30
1m30s
1:30

searching for 62 seconds can be entered as

62
62s
1m2
1m2s
1m02s
1:2
hm I wonder if we should match a shorter string than "duration".  Maybe we should accept any of:  duration, dur, time, length, len