#411 - added backup reminder modal to index page

...deadlocker8/budgetmaster/controller/BackupController.java

.../deadlocker8/budgetmaster/controller/IndexController.java

...n/java/de/deadlocker8/budgetmaster/settings/Settings.java

...de/deadlocker8/budgetmaster/settings/SettingsService.java

src/main/resources/languages/_de.properties

src/main/resources/languages/_en.properties

src/main/resources/static/js/accounts.js

src/main/resources/static/js/main.js

src/main/resources/templates/helpers/navbar.ftl

src/main/resources/templates/index.ftl

src/main/resources/templates/settings/settings.ftl

src/main/resources/templates/settings/settingsMacros.ftl