Added pane focus specific keybindings. refs #65

[geksilla]

ping @dvcrn, @spencerlyon2 to review.

[sglyon]

@geksilla this is a great start. Good work!

I have a couple of comments:

• SPC 0 goes to the tree view, but we can't use SPC # (for any number #) to get back out of it. This isn't particular to this PR, but just a reminder that we need access to proton-chain from non editor views.
• I would love to add these numbers to each pane so users know exactly where they are going when then do SPC #. I was thinking that maybe we could just push a small number icon to the top right of the tab-bar on each pane? Or we could do it on the bottom of the gutter? These options aren't great because they can both be toggled, but maybe that's just something the user has to live with if he toggles everything off?
• It would be great to have a single entry listed in the "prompt" area for [1-9] window N or something like that. Right now we have 10 of them for window 0 through 9 and it overflows that area.

[sglyon]

Do we need this to be its own function, or could we jsut use panes/focus-on-item in place of select-window-fn in the keybindings map?

[geksilla]

:fx should be a function, so I wrap panes/focus-on-item into function that returns function + window number as argument.

[sglyon]

Isn't panes/focus-on-item a function though?

[sglyon]

Ahh I see it. Nevermind. Haha sorry for being slow here

[geksilla]

regarding first comment there is issue #40. I'll try to fix that in another PR.
Agree with label [0-9], added 10 labels for spacemacs consistency, also needs to revisit chain method to achieve this.

[dvcrn]

Very cool PR! Can't wait to give this a shot. Is there anything you want to add? Otherwise I'll merge this now

[geksilla]

@dvcrn nothing to add for now. I would like to add single label [0-9] instead of 10, but it requires do some refactoring for keybindings and don't want to break things for now. I'll try in another PR if you don't mind.

[dvcrn]

👍