changed check style severity from error to warning

changed check style severity from error to warning in order to prevent
build errors cause of check style warnings
Adjusted pom

changed check style phase to install, to support eclipse and show
Checkstyle warnings at the end of the build. Build won’t fail because
of check style errors
formating.... :)
PHOT-23:  new dummy entities: image, album, category. without relations
PHOT-23:  rename entity Category to SysCategory
PHOT-50: new attribute for userProfile entity, firstname and surname
PHOT-23: collection and image entity with dao test and relations
PHOT-23:  new relation entity CollectionCategories and package-info
PHOT-23:  new entity showcase with relation to collection
PHOT-23:  new entity relation between user and image
Adjusted data model
Major refactoring
PHOT-24: new CategoryDAO and test getCollectionByUser
added new manager classes
added collection manager
PHOT-49: enhance register and login. Encrypt password with BCryptPasswordEncoder