Modify agent show view

OSRA-257 #Code-Review
https://osraav.atlassian.net/browse/OSRA-257

Modify display of sponsor information on assigned user's page as per client's specification:
- display active and inactive sponsors in separate panels in User show view
- only display the number of actively sponsored orphans for each active sponsor in User show view
- only display the number of active assigned sponsors in User index view

Under the hood:
- refactor several Cucumber step definitions for broader usage and/or robustness
- implement model methods and scopes to improve abstraction level and robustness