Refactor Charon database syncing and CharonSession object methods

See the actual reset code [here](https://github.com/NationalGenomicsInfrastructure/ngi_pipeline/pull/62/files#diff-b0ab78c2bbcb2d4eaf1d55f239c34f5dR177) and [here](https://github.com/NationalGenomicsInfrastructure/ngi_pipeline/pull/62/files#diff-b0ab78c2bbcb2d4eaf1d55f239c34f5dR57).