don't use Blockly at all on editCode levels

Previously, editCode levels still kept a div around called Blockly, loaded the blockly-core vendor.js, and injected Blockly into the page (while keeping it hidden).

I cleaned this up now so BlocklyApps.usingBlockly is the opposite of BlocklyApps.editCode and we only do Blockly things inside BlocklyApps.usingBlockly.
I'll at least add a comment. Theoretically, we could have yet another type (besides Blockly and Droplet), such as the plain ace editor. In which case, they wouldn't be mutually exclusive. I like the suggestion of usingDroplet, but am concerned about it being different from the level parameter called editCode (maybe I should change all of those too)