Make bar toggle-able per monitor-view combination

[Fuco1]

Make the status bar toggle-able per-view, not only per-monitor. This is useful with full-screen apps, such as virtualbox or spotify where I don't want to see the status bar on the top.

I'd like some comments on the current approach... it's a hack but with very minimal impact on the existing code so I quite like it. At first I tried to replace all the mentions of the Monitor_X_showBar but that proved a bit more troublesome. However, I'm not so familiar with the internal architecture to be 100% sure.

Thanks!