Fixies and changes in defaultUnixGroupName

- remove preferredDefaultUnixGIDs_namespace module
- rename prefferedUnixGroupName_namespace to preferredUnixGroupName_namespace
- fix some variable names
- add behavior when resource or group with right groupName has no GID in this namespace
- fix some dependencies
- add checkAttributeValue method for virt_defaultUnixGID module
- fix setAttributeValue method for virt_defaultUnixGID module
- use better description for basicDefaultGID
- and some minor typo fixies