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.