Plugin loading errors are app errors.

Change-Id: I71f3a6fb702a7e2935c28db37be1e03623c469f0
Reviewed-on: http://gerrit.dmdirc.com/3227
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/plugins/PluginInfo.java

@@ -610,7 +610,7 @@ public class PluginInfo implements Comparable<PluginInfo>, ServiceProvider {
             } catch (LinkageError | Exception e) {
                 lastError = "Error in onLoad for " + metaData.getName() + ":"
                         + e.getMessage();
-                Logger.userError(ErrorLevel.MEDIUM, lastError, e);
+                Logger.appError(ErrorLevel.MEDIUM, lastError, e);
                 unloadPlugin();
             }
         } else {