Add timeshifted column header dynamically

Instead of adding duplication in the Stagecraft response, we should
dynamically the generate the header for columns in the same way that
we do for the linelabel.
Fix student finance JSON stub

Regression introduced in https://github.com/alphagov/spotlight/commit/64e3f996e42719a9a4b732aa154eacf6d1695dfa#diff-cc691fbdfd80a34511f61d12a7583967L216