Changes due to Sonar
Simplify request mappings in application controller

* Use parent request mapping on class level.

* Remove unnecessary constants.
Simplify application controller and remove obsolete service methods

* Combine application controller methods that were separated to methods with
  year parameter and to without year parameter.
Clean up of application validator

* Add validator for comments and remove logic from application validator.

* Application validator has now only 'validate' method public for
  validation of applications for leave.
Clean up of entities: remove persisted property year from Account
Remove deprecated rep column from application for leave entity
Persisti enum values in application entity now as string instead of number
Simplify enums by removing artificial property key attributes
Convert persisting of status in comment entity from enum number to string
Remove unnecessary property progress from comment

* Progress can be represented by status property too.
Replace simple string representation of commenting person by reference

* The reference to the commenting person should be persisted in the
  comment table instead of a simple string.

* refs #17614
Enable showing gravatars in progress comments

* In progress of applications for leave and sick notes the comments
  are now displayed with the gravatar of the commenting person.

* refs #17614