Search "Next"/"Previous" result in an alignment from the selected region

Required changes:

1. When selection is changed in the Alignment Editor after search results, the "Results" label should be updated: "Results: -/total_num".
2. "Previous" and "Next" buttons should find a result previous/next to the selection left upper corner.

Scenario:

1. Open "COI.aln".
2. On the "Search in Alignment" options panel tab input "ACGT" pattern.
   Expected result: 7 results are found, the first result is selected in the sequence area (row 3, coords 419..422).
3. Select another region in the sequence area - a character in row 7, coord 2.
4. Click on the "Next" button.
   Expected result: the label is updated as follows "Results: 4/7", region row 7 coords 70..73 are selected in the sequence area.