Abstract payment integration

Right now, Strike is hard coded into the fn: `main.py/abbot()`

Goal:
- abstract the Strike class into a `Payment` class such that it can handle any number of possible payment integrations
- examples:
    - [x] Strike
    - [ ] ~OpenNode~
    - [ ] ~LNBits~
    - [ ] ~Voltage~
    - [ ] ~Home node~
    - [ ] ~Cloud node~
    - [ ] ~What else?~
    