improvement(popup): show shortcuts in the tooltips

[WofWca]

Problem

We have a lot of shortcuts, but discovering them is hard - they're only mentioned on the options page, and are hard to read.

Soultion

For each control, show the shortcuts for it.

Perhaps we could start by simply listing the default shortcuts, and not dynamically fetching them from settings.

Also let's see if we can add aria-keyshortcuts.