#455 - added tests for determination of files to delete

pom.xml

...de/deadlocker8/budgetmaster/database/DatabaseService.java

...deadlocker8/budgetmaster/settings/SettingsController.java

...cker8/budgetmaster/unit/database/DatabaseServiceTest.java

...deadlocker8/budgetmaster/unit/helpers/LoggerTestUtil.java

src/test/resources/backups/empty/.gitkeep

...ckups/three/BudgetMasterDatabase_2020_03_07_14_10_50.json

...ckups/three/BudgetMasterDatabase_2020_03_08_13_10_50.json

...ckups/three/BudgetMasterDatabase_2020_03_08_14_10_50.json