refactor: introduce better class structure for better testability

...x/cisd/authentication/file/FileAuthenticationService.java

...systemsx/cisd/authentication/file/FileBasedLineStore.java

...java/ch/systemsx/cisd/authentication/file/ILineStore.java

...java/ch/systemsx/cisd/authentication/file/IUserStore.java

...systemsx/cisd/authentication/file/LineBasedUserStore.java

...temsx/cisd/authentication/file/PasswordEditorCommand.java

.../java/ch/systemsx/cisd/authentication/file/UserEntry.java

...emsx/cisd/authentication/file/LineBasedUserStoreTest.java

...a/ch/systemsx/cisd/authentication/file/UserEntryTest.java