Clicking on a row should (un)highlight it (until refresh)

Clicking on a row should highlight it, and clicking again restore the background color back to white; it should be possible to highlight many different rows at once. This way users will be able to select those merges that they find interesting when they look at the list, and then easily find back to them without having to remember their name.

In order for this to be efficient, the feature described in bug 161762 needs to be implemented first. I'll try to work on both once I finish exams (next week).