More robust target detection in XML

[Gama11]

Currently, HTML5 builds break if there's an env variable called hl due to if="hl" in the XML:

@jgranick had some ideas to make this more robust:

but perhaps we should just define "target-" defines instead or "target:" if="target-hl" or if="target:hl"

[player-03]

Haven't tested it, but from the code I'm pretty sure you can write if="${targetType==hl}" if you want certainty. Except it only works for XML projects, and HXP projects are out of luck.

I think what needs to happen is ProjectXMLParser.initialize() needs to go in HXProject so that all projects will play by the same rules.