Add group setdisplayname command (#493)

sponge/src/main/java/me/lucko/luckperms/sponge/managers/SpongeGroupManager.java

@@ -288,4 +288,29 @@ public class SpongeGroupManager implements GroupManager, LPSubjectCollection {
     public void suggestUnload(String identifier) {
         // noop
     }
+
+    @Override
+    public Group getByDisplayName(String name) {
+        // try to get an exact match first
+        Group g = getIfLoaded(name);
+        if (g != null) {
+            return g;
+        }
+
+        // then try exact display name matches
+        for (Group group : getAll().values()) {
+            if (group.getDisplayName().isPresent() && group.getDisplayName().get().equals(name)) {
+                return group;
+            }
+        }
+
+        // then try case insensitive name matches
+        for (Group group : getAll().values()) {
+            if (group.getDisplayName().isPresent() && group.getDisplayName().get().equalsIgnoreCase(name)) {
+                return group;
+            }
+        }
+
+        return null;
+    }
 }

sponge/src/main/java/me/lucko/luckperms/sponge/model/SpongeGroup.java

@@ -151,8 +151,7 @@ public class SpongeGroup extends Group {
 
         @Override
         public Optional<String> getFriendlyIdentifier() {
-            String rawDisplayName = parent.getRawDisplayName();
-            return rawDisplayName.equals(getIdentifier()) ? Optional.empty() : Optional.of(rawDisplayName);
+            return parent.getDisplayName();
         }
 
         @Override

sponge/src/main/resources/luckperms.conf

@@ -89,12 +89,6 @@ world-rewrite {
 #  world_the_end="world"
 }
 
-# Rewrites group names. The underlying name of the group does not change, just the output in
-# commands / placeholders / Vault.
-group-name-rewrite {
-#  default="Member"
-}
-
 # Controls how temporary permissions/parents/meta should be accumulated
 #
 # The default behaviour is "deny"