#128 - Add language chooser to settings

src/de/deadlocker8/budgetmaster/logic/Settings.java

...de/deadlocker8/budgetmaster/logic/utils/LanguageType.java

src/de/deadlocker8/budgetmaster/logic/utils/Strings.java

src/de/deadlocker8/budgetmaster/resources/_de.properties

src/de/deadlocker8/budgetmaster/resources/flags/english.png

src/de/deadlocker8/budgetmaster/resources/flags/german.png

src/de/deadlocker8/budgetmaster/ui/cells/LanguageCell.java

...de/deadlocker8/budgetmaster/ui/controller/Controller.java

...ocker8/budgetmaster/ui/controller/SettingsController.java

...r8/budgetmaster/ui/controller/SplashScreenController.java

src/de/deadlocker8/budgetmaster/ui/fxml/SettingsTab.fxml

src/de/deadlocker8/budgetmasterserver/main/_de.properties