Refactor the gocui layout into a controllable abstraction

[wagoodman]

Currently the layout function (

dive/ui/ui.go

Line 186 in 993be8d

func layout(g *gocui.Gui) error {

) is mostly hardcoded and does not allow for dynamically changing the layout easily (or swapping out the layout entirely). This will be useful when adapting the UI for #52.

Additionally, while refactoring, errors during gocui actions should be reported up to the UI object and log accordingly. This will make problems like seen in #225 more visible.

[wagoodman]

addressed in #256