Scroll blockly

@kadst43 Allows scrolling vertically in the blockly interface, and for screens shorter than the default blockly height, makes the interface the same height as the window.

EDIT: Trouble with the height changing is that, if a user opens the app in a smaller screen, then resizes to a larger screen, the interface will stay the same shorter height. 
If we're going to hardcode, to the extent that it's feasible let's put the magic numbers in yaml rather than burying them in js.  So in yaml we'd have a parameter like maxBlocklyWindowHeight: 812.