#269 - categories can now be added; added validation;

...java/de/deadlocker8/budgetmaster/advices/ColorAdvice.java

...adlocker8/budgetmaster/controller/CategoryController.java

...n/java/de/deadlocker8/budgetmaster/entities/Category.java

src/main/java/de/deadlocker8/budgetmaster/utils/Helpers.java

.../java/de/deadlocker8/budgetmaster/utils/Notification.java

.../de/deadlocker8/budgetmaster/utils/NotificationLevel.java

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

...eadlocker8/budgetmaster/validators/CategoryValidator.java

src/main/resources/languages/_de.properties

src/main/resources/languages/_en.properties

src/main/resources/templates/newCategory.ftl