#937 Add option for AuthMe to run in sync

- Create BukkitService#runTaskOptionallyAsync and BukkitService#scheduleSyncTaskFromOptionallyAsyncTask whose behavior depends on a new setting
- Use the new methods where applicable
- Declare events async or sync depending on the new setting

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

@@ -55,7 +55,7 @@ public class ChangePasswordAdminCommand implements ExecutableCommand {
 
         // Set the password
         final String playerNameLowerCase = playerName.toLowerCase();
-        bukkitService.runTaskAsynchronously(new Runnable() {
+        bukkitService.runTaskOptionallyAsync(new Runnable() {
 
             @Override
             public void run() {

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

@@ -55,7 +55,7 @@ public class RegisterAdminCommand implements ExecutableCommand {
             return;
         }
 
-        bukkitService.runTaskAsynchronously(new Runnable() {
+        bukkitService.runTaskOptionallyAsync(new Runnable() {
 
             @Override
             public void run() {
@@ -80,7 +80,7 @@ public class RegisterAdminCommand implements ExecutableCommand {
                 ConsoleLogger.info(sender.getName() + " registered " + playerName);
                 final Player player = bukkitService.getPlayerExact(playerName);
                 if (player != null) {
-                    bukkitService.scheduleSyncDelayedTask(new Runnable() {
+                    bukkitService.scheduleSyncTaskFromOptionallyAsyncTask(new Runnable() {
                         @Override
                         public void run() {
                             limboCache.restoreData(player);

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

@@ -41,7 +41,7 @@ public class SetEmailCommand implements ExecutableCommand {
             return;
         }
 
-        bukkitService.runTaskAsynchronously(new Runnable() {
+        bukkitService.runTaskOptionallyAsync(new Runnable() {
             @Override
             public void run() {
                 // Validate the user
@@ -68,7 +68,6 @@ public class SetEmailCommand implements ExecutableCommand {
 
                 // Show a status message
                 commandService.send(sender, MessageKey.EMAIL_CHANGED_SUCCESS);
-
             }
         });
     }