Admin UI: bulk of changes

https://issues.jboss.org/browse/AGPUSH-748
Use Angular's "controller as name" syntax to avoid scoping problems

https://issues.jboss.org/browse/AGPUSH-986
Refactor pushApplication.js service to expose only endpoint methods + split into separated files

https://issues.jboss.org/browse/AGPUSH-1096
Allow to generate push-config.json for several selected variants at once