remove clearSelection(), rename selectAndHighlightCode()

[cpirich]

• clearDropletAceHighlighting() cleared the ACE editor selection in addition to clearing highlights. Presumably, this was originally done because it was the function to "clear" what was done in selectAndHighlightCode(), which used to both select AND highlight the code. Now, that function only does highlighting (and no selection). Renamed that function to highlightCode() to be more clear and removed the ACE editor clearSelection() call from clearDropletAceHighlighting()

Since we recently starting calling this function once per executeInterpreter(), it was preventing students from being able to select code while running

Other places where clearDropletAceHighlighting() is called, that will no longer clear ACE selection:

• Pressing the Reset button in an app
• Stepping through code in the debugger and ending up outside of "user code"

In both places, it feels like an improvement to avoid interfering with the ACE editor selection.

[islemaster]

Looks good. Thanks for the detailed description on this change!