Fix for parameter focusing

Fixes #414

Try it here: https://dl.dropboxusercontent.com/u/76236043/scratch/parameterFocus.swf

I also changed the code so when you re-open a procedure to edit it, the first parameter receives keyboard focus, not the first text object as the code was previously doing.

(My first bugfix, yay!)
Might be cleaner just to do `BlockArg(o).startEditing();`.