More effect changes to new format and realtime preview

Main effect host processing extended to support generate
effects and sync locked tracks.

Ladspa updated to utilize new generate support.

I'll address Analyze plugins when I get to the SBSMS ones.

Shared and private config changes are flushed immediately.

Cancel button restored to VST and Ladspa dialogs.  This
also restores the ESC button functionality.

Current parameters saved with Apply or Ok clicked...not
when Audacity ends.

Ladspa and VST effects with that reports no input and
no outputs are now ignored.

Ladspa effects providing a latency value is now handled.

Ladspa generator effects now use the TimeTextCtrl for
specifying duration.

src/effects/lv2/LV2Effect.cpp

@@ -79,7 +79,7 @@ LV2Effect::LV2Effect(const LilvPlugin *data,
    fInBuffer = NULL;
    fOutBuffer = NULL;
 
-   mLength = 0;
+   mDuration = 0;
 
    // Allocate buffers for the port indices and the default control values
    int numPorts = lilv_plugin_get_num_ports(mData);
@@ -386,7 +386,7 @@ bool LV2Effect::PromptUser()
          return false;
       }
 
-      mLength = dlog.GetLength();
+      mDuration = dlog.GetLength();
       mNoteLength = dlog.GetNoteLength();
       mNoteVelocity = dlog.GetNoteVelocity();
       mNoteKey = dlog.GetNoteKey();