Remove indentation of textarea contents

[balderdash]

This only applies to local development, but if you're running levelbuilder in mode and edit a level with some textarea fields (e.g. animation json in gamelab, toolbox blocks xml in blockly levels, etc.), the contents will be indented a few extra spaces. If you hit save, it'll add that whitespace to the level's property, and the next time you open the edit page it'll be doubly indented!

This PR uses haml's whitepsace preservation operator to de-indent the contents of these textareas.

[Hamms]

Any idea why this only happens locally, and not on the actual levelbuilder server?

[balderdash]

I'm pretty sure it's because haml is running in ugly mode on levelbuilder (i.e. it doesn't nicely indent the generated html), but I can't find where that's configured.

[Hamms]

Ahh, that makes sense. I'm just paranoid about this change affecting the behavior of the levelbuilder server, but it sounds like that shouldn't happen.

We should still keep an eye out for this PR hitting levelbuilder, and double-check that all is still fine when it hits.