Add selections of multiple rows/cols

[zoecastillo]

Following the process of click-selecting a single row/col, selecting multiple rows/cols via brush-selection should be possible.
All selected rows/columns should be returned and selected region should be highlighted.

[jkanche]

@OssamaRafique I just noticed the state is not being reset somewhere properly, to reproduce this issue

Step 1: click on "enable highlight", select a few columns/rows, I clicked on C9-11 and r4-6

Step 2: clear highlights by clicking the button

Step 3: try to highlgiht the same rows from Step 1, I would have to double click on the labels. for others single-click works.

[OssamaRafique]

@jkanche Thanks for pointing this out, PR is up #13

[jkanche]

Thanks for the update