GMS client improvements

.gitignore

gms-client/gms-cli/gms.properties

gms-client/gms-cli/pom.xml

...client/gms-cli/src/main/java/it/inaf/ia2/gms/cli/CLI.java

gms-client/gms-client-lib/pom.xml

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

...rc/main/java/it/inaf/ia2/gms/client/GmsClientBuilder.java

...rc/main/java/it/inaf/ia2/gms/client/call/BaseGmsCall.java

...ain/java/it/inaf/ia2/gms/client/call/DeleteGroupCall.java

...n/java/it/inaf/ia2/gms/client/call/HttpClientWrapper.java

...va/it/inaf/ia2/gms/client/call/HttpClientWrapperTest.java

.../it/inaf/ia2/gms/client/call/MockedHttpClientWrapper.java

gms-client/gms-client/pom.xml

...lient/src/main/java/it/inaf/ia2/gms/client/GmsClient.java

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

.../main/java/it/inaf/ia2/gms/client/call/AddMemberCall.java

...n/java/it/inaf/ia2/gms/client/call/AddPermissionCall.java

...ain/java/it/inaf/ia2/gms/client/call/CreateGroupCall.java

...ain/java/it/inaf/ia2/gms/client/call/DeleteGroupCall.java

.../it/inaf/ia2/gms/client/call/GetGroupPermissionsCall.java