♻️ Extract EF config from RulesContext

[jackreimers]

Cc: @danielmackay

Hi

Pain

Currently all of the EF config is stored in the DbContext.
Dan suggested it should be moved out into a seperate class to keep the DbContext tidy as part of his review on #150.
The names of model classes should also have consistent suffixes, i.e. Model, Result or no suffix

Acceptance Criteria

The EF configuration code is extracted from RulesContext and the database access still works as expected.

Thanks!

### Tasks
- [ ] Extract EF config to a seperate class
- [ ] Make names of model classes consistent (i.e suffixes Model, Result)