Moar renamings
These commits introduce:
- client/server API validators, so renamings can be easier and caught at runtime :) (also make the API slightly better)
- a fix for assertions during testing
- renames Category.title to label
- renames Account/Access.bank to vendorId; I've tried to be cautious with this one and I've tested it thoroughly, but it's almost certain that there's going to be missing spots, because grepping for "bank" in Kresus is a sad endeavor. We can still open new MRs for missing spots :)