#JC-1184 Refactoring of activation process

- Added/corrected JavaDocs to the classes and Spring Context
- Added logging to cover all the cases related to account activation
- Corrected the ukrainian translation of activation error message, it was wrong form all the language perspectives
- Moved the plainPasswordAuthenticationManager from security-service-context.xml to applicationContext-service.xml because it's used only there and it can be declared as anonymous bean. Also removed an explicit parameter of plain password checker because it's the default one.