Throw clear error if the metadata.j script did not load and define 'zza.metadata'
Zza DevController offers more script file writing options
Used by prepareTestData to write Zza/breeze.metadata.js, the Breeze JS form of the metadata.
Zza.ExpressServer now prefers static content from its /public directory to static content in zza directory
This enables replacement/overriding of static content that would otherwise be loaded from zza folder