#1116 #1117 Add command usage hints and remove unused message keys

- Add usage message on argument mismatch where available
- Remove unused message keys
- Create tool task to search for a message key's usages and to find unused keys

src/test/java/fr/xephi/authme/message/MessagesIntegrationTest.java

@@ -89,7 +89,7 @@ public class MessagesIntegrationTest {
     @Test
     public void shouldFormatColorCodes() {
         // given
-        MessageKey key = MessageKey.UNSAFE_QUIT_LOCATION;
+        MessageKey key = MessageKey.LOGIN_SUCCESS;
 
         // when
         String[] message = messages.retrieve(key);
@@ -115,7 +115,7 @@ public class MessagesIntegrationTest {
     @Test
     public void shouldSendMessageToPlayer() {
         // given
-        MessageKey key = MessageKey.UNSAFE_QUIT_LOCATION;
+        MessageKey key = MessageKey.LOGIN_SUCCESS;
         Player player = Mockito.mock(Player.class);
 
         // when