Proposed level format change

Seeking feedback and comments on a proposed change in the custom level format. Since Blockly accepts its level definitions in a special XML format, we've kept this format the same when working with these aspects of the level definitions within our custom level editor. However, before this change these XML files weren't very readable in the exported level file itself, because it required escaped quotes and a single line of text in order to comply with the JSON format.

This proposal reverses the level format, wrapping the existing JSON config within an XML node, and allowing the special block entries to exist as XML on the outer layer. This allows the whitespace-formatted block definition XML to be quickly readable from the text file (and it will also play nice with syntax highlighting from IDEs such as RubyMine).