Initial support for Groups

Create separate object for Users and Groups (using same base class)
Check for uniqueness before adding new users and groups
Remove user_container from everything but add operations
Abstract out a number of functions that are common across users and groups
Make sure all strings passed in to be in a filter are checked
Add new error message: No modifications specified

ipa-admintools/ipa-usermod

@@ -54,7 +54,11 @@ def main():
         usage()
 
     client = ipaclient.IPAClient()
-    user = client.get_user_by_uid(args[1])
+    try:
+        user = client.get_user_by_uid(args[1])
+    except ipa.ipaerror.IPAError, e:
+        print "%s" % e.message
+        return 1
 
     if options.gecos:
         user.setValue('gecos', options.gecos)