set tmux status background/window-status-formats from powerline

Currently, the tmux-statusline background and formats are not set from powerline but from a separate .tmux.conf file. This means that the divider character is set separately, colors are set separately and the them can not really be configured all from powerline.

This solution is obviously very hacky and it sort of leaves the code looking worse. It does basically work, with one caveat. We have to constatly (in each call to render set the tmux attributes) This is bad both because it adds side effects to the call to tmux powerline and because it causes tmux to reset the current mouse selection for whatever reason. This could be alleviated a bit if we only set the attributes whenever config files change, but we would also need a way to set all of the attributes once at startup. This might involve adding a flag to the shell runner to force something like this that gets run once on tmux startup.

Anyway, I am happy to continue to try to bang this out, but I'm starting to feel like it might be too gross to merit inclusing.