added version conflict resoler and ivy support

Details:
- added Ivy support
- split models in seperate files
- added VersionConflictResolver (for resolving version conflicts like Ivy)
- made variants logic a field on loader engine, to make it easier to use new ones and also test
Merge branch 'master' of github.com:adept-dm/adept

Conflicts:
	build.sbt
	project/plugins.sbt