#437 Email uniqueness in admin command; finalization

- Check also in admin command that email is not already used
- Misc bug fixing (logic errors, changes lost during large merge)
- Use "email" and "setemail" as main labels for /authme subcommands

src/main/java/fr/xephi/authme/command/CommandInitializer.java

@@ -133,7 +133,7 @@ public final class CommandInitializer {
         // Register the getemail command
         CommandDescription.builder()
             .parent(AUTHME_BASE)
-            .labels("getemail", "getmail", "email", "mail")
+            .labels("email", "mail", "getemail", "getmail")
             .description("Display player's email")
             .detailedDescription("Display the email address of the specified player if set.")
             .withArgument("player", "Player name", true)
@@ -144,7 +144,7 @@ public final class CommandInitializer {
         // Register the setemail command
         CommandDescription.builder()
             .parent(AUTHME_BASE)
-            .labels("chgemail", "chgmail", "setemail", "setmail")
+            .labels("setemail", "setmail", "chgemail", "chgmail")
             .description("Change player's email")
             .detailedDescription("Change the email address of the specified player.")
             .withArgument("player", "Player name", false)

src/main/java/fr/xephi/authme/command/executable/authme/SetEmailCommand.java

@@ -33,6 +33,9 @@ public class SetEmailCommand implements ExecutableCommand {
                 if (auth == null) {
                     commandService.send(sender, MessageKey.UNKNOWN_USER);
                     return;
+                } else if (commandService.getDataSource().isEmailStored(playerEmail)) {
+                    commandService.send(sender, MessageKey.EMAIL_ALREADY_USED_ERROR);
+                    return;
                 }
 
                 // Set the email address