Implement risk level calculation changes (#136)

* changed local config that a high match can be generated via QR code, integrated it with the UI

* added the minRiskScore parameter to the ExposureConfiguration

* moved the persistence of the exposure summary in a dedicated worker to ensure execution

* added new backend app config and custom risk score calculation

* fixed static code checks and refactoring

* deleted possibility to customise app config in the tests

* added test fragment for risk level calculation

* static code check fixes

* refactored risk level calculation and added tests

* added exception if calculated risk score is above the max of the high risk score class