move-focus to accept name of pane

[danielb2]

right now the action move-focus command is fairly limited. if there are nested panes it can be difficult to navigate focus to a specific pane, and even with a relatively simple four pane layout, getting from lower right quadrant to top left would require two commands on CLI to do it programatically.

I propose new panes gets an index just like tabs do that can be used to refer to them so every pane has a number. this already aligns with go-to-tab

perhaps a go-to-pane would also make sense, but I think move-focus is already sufficient

action move-focus <direction|index|name> may be workable

[cristiand391]

GH issue: #2779