Don't allow hiding of an action if it's currently selected

[sbates-idrc]

Currently, you can hide the selected action, and still add it to the program even though it's hidden. Although C2LC-494 made it possible to manually fix the issue, we agreed to clean things up further:

1. The actions menu should display "Selected" next to the selected action
2. It should not be possible to hide the selected action
3. The modal should correctly display the selected command if it's changed using keyboard shortcuts while the modal is open

Steps to reproduce:

1. Begin with all actions visible
2. Select move forward
3. Open the simplification dialog
4. Hide the move forward action and close the dialog
5. Click on an add “+” in the program editor to add a move forward action to the program

Original Jira issue: https://fluidproject.atlassian.net/browse/C2LC-496