Defines a method to clear out the blockly workspace

Adds a method to clear out all of the blocks from the blockly workspace.

I tested this from the console, since this isn't exposed to the UI.

vwf.callMethod( roverID, "blocklyClear", [] )
Actually I did not.  If the change event fires then the topBlockCount and blockCount will be set.

I'll check now, and then remove those calls if they are not needed.