Per-window infoviews

Contrary to how I did this in #35, I think rather than switching between per-window and per-tab, we should always allow both, and always initialize a per-tab infoview on new tab and per-window infoview on new window, configurable whether these automatically open (default true for per-tab and false for per-window). Then it should just be a matter of "switching focus" from the tab infoview to the window infoview when the window infoview is opened and switching focus back to the tab infoview when the window infoview is closed.