Mid Sensitivity Calculator Back-end Refactor

Currently the sensitivity calculator comprises of two almost identical versions, one intended for regular users and one for SKA scientists allowed to modify variables other users should not change. This means there is a lot of duplicate code which makes maintaining the project more difficult. The duplicate code should be removed where possible by modularisation and re-organisation. Tests should be added before any changes are made to make sure any unintended changes are not made to the functionality during refactoring.

This back-end refactor should be completed before the front-end refactor described in SP-947