Add utility method to prefs setting to remove logic from UI

Issue CLIENT-26

Change-Id: Id1c32eb2e1b0b0be8a51563becaed0c1ff443180
Reviewed-on: http://gerrit.dmdirc.com/1834
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>

src/com/dmdirc/config/prefs/PreferencesSetting.java

@@ -21,6 +21,7 @@
  */
 package com.dmdirc.config.prefs;
 
+import com.dmdirc.config.Identity;
 import com.dmdirc.config.IdentityManager;
 import com.dmdirc.util.validators.PermissiveValidator;
 import com.dmdirc.util.validators.Validator;
@@ -304,4 +305,15 @@ public class PreferencesSetting {
                 && (validator == null || !validator.validate(current).isFailure());
     }
 
+    /**
+     * Does the specified identify have this value set?
+     *
+     * @param identity Identity to check
+     *
+     * @return true iif the setting is present
+     */
+    public boolean existInIdentity(final Identity identity) {
+        return identity.hasOptionString(domain, option);
+    }
+
 }