Add initial VNC quality setting

As discussed, a simple approach to add a bandwidth/quality option to VNC connections. For now 'high quality' is the default, until an adaptive setting is later provided.

I also found that the VNC-specific properties didn't appear to be getting saved, and I added a tiny .gitignore.

Naturally, let me know if you'd like things done other ways (perhaps an enum?), or preferred names for the options, and I'll make the changes.

Partly addresses #22 (closed).