Graphical version of the search query box

[sveinugu]

Inspired by the Finder "find" query specification:

Some thoughts:

• In contrast to the Finder query, TrackFind query parameters should not be modifiable
• There should be no plus icon, only a minus icon.
• There should be a visual solution for the boolean logic, though. In its simplest form, this will be one or two indicators in the beginning of each item: (AND, AND NOT, OR, OR NOT) or (AND, OR) [NOT]
• One improvement is to be able to edit the boolean logic with some selection mechanism
• One can also imagine more complex queries visualized hierarchically somehow.
• The user should be able to switch between graphical and text mode. If the text mode cannot be transformed into graphical mode, a proper error should appear.