Allow rerunning subset of tests from Run window

[vmallet]

Once a set of tests has run and the results are showing up in the Run window, it would be good to be able to re-run some tests. Some ideas:

• Right click on specific test and choose "re-run test"
• Be able to command-click several tests and right-click "re-run selected tests"
• Gutter button to "rerun all failed tests"