We've been sometimes using lo and sometimes using my slices package, and we need to pick one
for consistency. Lo is more extensive and better maintained so we're going with that.
My slices package was a superset of go's own slices package so in some places I've just used
the official one (the methods were just wrappers anyway).
I've also moved the remaining methods into the utils package.
Previously we applied a right-align on the first column of _all_ menus, even though we really
only intended for it to be on the first column of the keybindings menu (that you get from pressing
'?')
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.
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
