add custom saved search filtering - also advanced search

[DancingDirty]

after #13 is implimented (tags) I got an idea:

• in the filter area there should be a "saved searches" where someone could save a search. Clicking on the saved search would filter the torrent list as the user wants.
• There should be also "add advanced search" which would allow for constructing advanced filtering.
• The window of "add advanced search" would have filtering like "older than", "newer than" also "includes tag/word", "does not include tag/word" etc and have a AND OR system thats easy to conprehend, look how the window would look like:
  
  [the image is from other project, I will update it with more relevant to qbt later on]