RegionSelector refactoring

In the UGENE-3267 issue the new class SimpleRegionSelector was created: it contains only start-end line edits. As a result it copies some of RegionSelector code.

Note that region selector is used in many places. So there should be a flexible way to manage all possible selectors:

• simple start-end selector (exclude region in Find Enzymes dialog)
• old horizontal region selector (e.g. Find Repeats dialog)
• vertical region selector (Smith-Waterman Find Pattern)

Refactor the code to make it easy to deal with any kind of selector and remove double code.
Also improve the logic of error notification in case of problems with the region: the idea of red highlighting and the tool-tip was mentioned in the team.