workspaces: handle move to workspace

add, remove window: abstract functionallity further

add `addWindow()` and `removeWindow()` functions, that figure out on
their own, wether they are deleting the master or a stack window. this
way the window manager doesn't have to do this every time he wants to
add/remove a window

workspaces: now hold their index, as seen in gnome

code: abstract workspaces into seperate class

code: reorder code

tiling: support mfactor, also supprts mfactor/workspace

extension: fix cleanup code

shell: support multiple workspaces

tiling: rotate the stack

code: abstract remove and add window to own methods

tiling: support removing windows

adhere to styleguide and add comments

initial, spawning works