Refactor LSF parser
Refactor LSF parser

- Reorder imports to PEP 8.
- Rename mapping_lsf_5678 to just mapping_lsf as support for 9 has been
  added and there are quite a few numbers now.
- Change instances of 'assert' used to test negative values to 'if: raise'
  and add check for stop time less than start time.

tofu-rocketry/apel,stfc/apel,tofu-rocketry/apel,stfc/apel,apel/apel,apel/apel