Add scope definitions to the model class

See https://github.com/strongloop/loopback/issues/454
Pass options into scope
Merge branch 'fabien-feature/plugins'
Bump version
Fix the test case so that it works with other DBs
Merge branch 'release/2.3.0' into production
Merge tag 'v2.3.0'

2.3.0
Fix a name conflict in scope metadata
Merge branch 'release/2.3.1' into production
Merge tag 'v2.3.1'

2.3.1
Merge branch 'master' into fix/refactor-modelto
Make lookupModelTo follow previous logic