Add system updates

[leolost2605]

Some strings might need some refinement

Rquires elementary/settings-daemon#88

[danirabbit]

Hey so I was playing around with a different design here: https://github.com/elementary/switchboard-plug-about/pull/281

[danirabbit]

Yay, I'm glad we're back on one branch haha. I'll make another commit real quick to add back the cancel button!

[danirabbit]

Okay, done pushing, I'll use branches if I want to propose something else, you can take back over :sweat_smile:

[danirabbit]

@leolost2605 cleaned up some button stuff https://github.com/elementary/switchboard-plug-about/pull/283

[leolost2605]

So I think I've got everything in that I wanted. Only missing from my side is an info button for package details and error info. Also I'm sure there are some refinements that can be done :)

[danirabbit]

Yeah this is hella good! I'll put together a branch to show package details

[leolost2605]

Let's go then! 🚀