Allow to re-open GitSavvy page (status / branches, ...) with keyboard shortcut

[philipp-tailor]

When I use the keyboard shortcut to close one of the GitSavvy pages (CMD + W on the Mac), and then want to re-open the close tab like any other document with the keyboard shortcut (on the Mac that's CMD + Shift + T), then the GitSavvy view is not re-opened. This is a bit unexpected and makes re-opening an accidentally closed GitSavvy page harder. I'm not sure whether that's a limitation of the Sublime extension APIs.

[kaste]

Möglich and probably useful. Technically simple but a bit cumbersome because we need to handle every GitSavvy view, write down its state, and then implement the cloning, or undoing, on our own.