Every time a window is closed its size is saved for newer windows. If multiple windows are closed at the same time, only the active one will save its size (if any window is active).
There are a few design questions left, like what to do when the user quits the application, say using the "Quit" option in the dash. In this case since there is no active window nothing will be saved. I personally think this is a good enough behavior.
Now the code will spawn newer windows with the size of the currently active window, if any, otherwise will fall back to the gsetting.
Fixes: #120 (closed)