Auto split master window, order slaves in new ways, center multiple stacks

[Dregu]

Some new features to mainly make me happy, merge if you wanna. Not super interested in making this perfect, seems good enough for me right now if no huge issues arise, but I haven't really tested anything yet...

I was mainly annoyed by existing window positions being too chaotic when increasing stack size and being forced to layouts like 1-2-1 when I wanted 1-1-2.

Sorry the diff is funny, but no one seemed to be using that clang-format and I did...

• Added option to auto_promote slave window to master when slave area gets too crowded (fixes Possibility to split master window #15)
• Added option to auto_demote extra master window when slave area is less crowded again
• Added new ways to order slave area, like column first, right to left
• Added xfact to center any number of stacks (fixes [FEATURE] extra margin when only 2 windows #18)
• Added some dispatchers for the new things
• Added fixes to actually override things with layoutmsgs, which seemed impossible
• Mouse stuff is probably even more messed up than before

Playing around with auto_promote=8 auto_demote=6 order=rc and others:

nstack-auto-order-8MB.mp4

[smallstepman]

thank you it's amazing