We want to show an error when the user tries to invoke an action that expects only
a single item to be selected.
We're using the GetDisabledReason field to enforce this (as well as DisabledReason
on menu items).
I've created a ListControllerTrait to store some shared convenience functions for this.
This requires us to change the 'v' keybinding for paste to something else,
now that 'v' is used globally for toggling range select. So I'm using
'shift+v' and I'm likewise changing 'c' to 'shift+c' for copying, so
that they're consistent.
We will need to clearly communicate this change in keybindings.
We have not been good at consistent casing so far. Now we use 'Sentence case' everywhere. EVERYWHERE.
Also Removing 'Lc' prefix from i18n field names: the 'Lc' stood for lowercase but now that everything
is in 'Sentence case' there's no need for the distinction.
I've got a couple lower case things I've kept: namely, things that show up in parentheses.
