Move optional requirements to separate files.
Use itertools.product instead of custom code.
Improve warnings.
Fix bug when Data subset is given.
Code pruning and improvements.
Remove warning after receiving proper data.
Improve sql code.
Merge pull request #104 from astaric/requirements

Move optional requirements to separate files.
Merge pull request #105 from lanzagar/mosaic

Refactor Mosaic Display
Added missing priority tags.
Removed dependency on orangeqt from scatter and box plot widgets.
Expunge superfluous semicolons.
Delete unnecessary line.