#4 Implemented invited registration

...t-lib/src/main/java/it/inaf/ia2/gms/client/GmsClient.java

.../inaf/ia2/gms/client/call/AddInvitedRegistrationCall.java

gms/src/main/java/it/inaf/ia2/gms/authn/SecurityConfig.java

...n/java/it/inaf/ia2/gms/controller/HomePageController.java

...naf/ia2/gms/controller/InvitedRegistrationController.java

...a/it/inaf/ia2/gms/controller/JWTWebServiceController.java

...ain/java/it/inaf/ia2/gms/exception/NotFoundException.java

...a/it/inaf/ia2/gms/manager/InvitedRegistrationManager.java

...a/it/inaf/ia2/gms/persistence/InvitedRegistrationDAO.java

...main/java/it/inaf/ia2/gms/persistence/MembershipsDAO.java

...t/inaf/ia2/gms/persistence/model/InvitedRegistration.java

...c/main/java/it/inaf/ia2/gms/service/GroupNameService.java

gms/src/main/resources/sql/init.sql

gms/src/main/resources/templates/invited-registration.html

gms/src/main/resources/templates/registration-completed.html