Fix inconsistencies in progress reporting (#2129)

Signal and setup events correctly
Eliminate possible races
Use a single event
Mark volatiles and reduce scope of waithandles
Common handler
100ms -> 50ms

ARMeilleure/Translation/PTC/PtcLoadingState.cs

@@ -0,0 +1,9 @@
+namespace ARMeilleure.Translation.PTC
+{
+    public enum PtcLoadingState
+    {
+        Start,
+        Loading,
+        Loaded
+    }
+}