Move similar config checks to a common function

'autoRegisterFloodgate' and 'autoLoginFloodgate' have the same possible
options, and they are checked against the player in the exact same way.
For example, if either one of them is set to isLinked, linked status is
checked in the same way, regardless of wether it's checked for login or
for registering.

bungee/src/main/java/com/github/games647/fastlogin/bungee/task/FloodgateAuthTask.java

@@ -57,7 +57,7 @@ public class FloodgateAuthTask
 
         // run login task
         Runnable forceLoginTask = new ForceLoginTask(core.getPlugin().getCore(), player, server, session,
-                isAutoLoginAllowed());
+                isAutoAuthAllowed(autoLoginFloodgate));
         core.getPlugin().getScheduler().runAsync(forceLoginTask);
     }