Add feature test for discrepencies on wage details

@jgumbley
Display discrepancy on wage-details page
Modify feature tests for wage details discrepancies
Create claim_service
Add claim entity
Create discrepencies in claim
Fix key names in discrepancies feature test
Use claim to surface discrepancies to controllers
Only accept weekly gross rate of pay

We can currently only match on weekly gross rate of
pay. This is obviously a hack. We will fix it going forwards
but in order to get the discrepancy view standing up
we're going with it for now.