Improve Tests for CommonsCard and ProfitsTable to Pass Mutation Testing

[rranu]

Currently mutation testing for the frontend results in 9 mutations consistently surviving. 2 of them relate to CommonsCard.js and the remaining 7 are from ProfitsTable.js. These files have not been changed in half-a-year or longer, so this is a legacy issue. Small improvements to the test-suites (as well as potentially fixing some Stryker disables) are in order.

• Fix month comparison testing for CommonsCard.js for November and December due to the naive use of +2 to the current month
• Either add stryker disable next-line BlockStatement: Unreasonable Mutation before line 17, or just take the following statement out of the else block (due to returns already leaving the function in other cases
• Add tests for ProfitsTable.js which check that accessors aren't changed