Go really doesn't like us doing anything inheritance-y: it does not support open recursion meaning
it's really hard to re-use code. As such, here we're falling back to conditional logic.
This fixes an issue where our ListContextTrait was calling FocusLine which was intended to be
overridden by ViewportListContextTrait, but the subclassed function wasn't being called. I'm
not actually sure how this went wrong given that it was working fine in the past, but at any rate,
the new code is easy to follow.
If a given menu item has an associated keybinding of 'enter', hitting enter won't actually execute
that item unless your cursor is on it. This creates confusion, and so we're going to use a strikethrough
style to communicate that the keybinding is reserved for something else.
When we use the one panel for the entire commit message, its tricky to have a keybinding both for adding a newline and submitting.
By having two panels: one for the summary line and one for the description, we allow for 'enter' to submit the message when done from the summary panel,
and 'enter' to add a newline when done from the description panel. Alt-enter, for those who can use that key combo, also works for submitting the message
from the description panel. For those who can't use that key combo, and don't want to remap the keybinding, they can hit tab to go back to the summary panel
and then 'enter' to submit the message.
We have some awkwardness in that both contexts (i.e. panels) need to appear and disappear in tandem and we don't have a great way of handling that concept,
so we just push both contexts one after the other, and likewise remove both contexts when we escape.
This begins a big refactor of moving more code out of the Gui struct into contexts, controllers, and helpers. We also move some code into structs in the
gui package purely for the sake of better encapsulation
