[idea] Give visual clue that we are in maximized mode.

[trusktr]

Currently, there's no visual cue. Someone could forget that they maximized a pane, then they might try and make a new split or something, and possibly mess up the state (not sure if all possible cases have been tested, but a visual clue would remind the user to un-maximize before continuing with an action).

[trusktr]

I just ran into the problem, I put an Atom instance aside, and when I came back I totally forgot that I left a pane maximized and went to re-open a bunch of stuff all over again.

[tomcoakes]

I tackled this a while back. It's still there in an open pull request - #17