[Split Window]: instead of 3 shortcuts: 2 shortcuts with do/undo

[ralf3u]

at the moment there are 3 shortcuts (the first shortcut to split horizontally, the second to split vertically, and the third for undo);
2 shortcuts would be better with do/undo; so, to split window with one shortcut would be the same shortcut to undo split the window


even better would be a 2x if-undo for each shortcut, like this:

shortcut for split up and down:
if window is splitted left and right, then: undo; if window is splitted up and down, then: undo, else: split up and down

shortcut for split left and right:
if window is splitted up and down, then: undo; if window is splitted left and right, then: undo, else: split left and right

[elextr]

Split window is a core plugin in the Geany repository, moved to that repository