Improved state/preset persistence in VST3

[dmsplugins]

I have made some modifications that improve state/preset persistence in VST3 builds (only tested on Windows). These seem to work consistently/well with plugins using chunks but not as well when using MakePreset() or MakePresetFromNamedParams()

• .vstpreset files can be imported/exported using Reaper's plugin preset utility menu, whereas they were greyed-out before.

• .vstpreset files created in Sonar are compatible with ones created in Reaper and vice versa. I'm not sure about FLStudio as I only have a demo that is restricted in its ability to save..... .vstpreset files load well though. Other than SaviHost, those are the only hosts I've tested.

• When kNumPrograms is greater than 1, the bank state is saved/recalled in both host project and .vstpreset files.

• fixed an issue where the plugin would crash when cancelling a "DumpPresets" operation.

• Modified IPlugChunks example project to demonstrate the improvements.