Rewrote a lot parts to extract 'payments' table (+ handling) into own extension:

Rewrote a lot parts to extract 'payments' table (+ handling) into own extension:
- Tried to avoid JOINs where possible to instead load data with getters from
  cache
- Renamed many array elements for payment data to match with database columns
- Used more EL code for payment data
- TODOs.txt updated