Use PackageCard in Available Updates panel

[mgarciaisaia]

PackageCards show Update buttons whenever there are new versions (even in other panels).

They cards aren't half-wided, but they work better than the previous view.

Fixes #499
Fixes #529
Supersedes #539

[mnquintana]

Awesome, thanks so much for this! I did find a few issues though:

• Package card doesn't change state when clicking the uninstall button
  • With disabled packages, the package card doesn't change state at all
  • Uninstalling enabled packages leaves a package card with an update button
    • Clicking that update button re-installs the package and updates it

Do you think you could take a look at these cases (and add specs for them)?

[mgarciaisaia]

I sure can try.

May those be PackageCard's issues - ie, a separate issue?

I'll try to review this later.

[benogle]

I love this idea. I think we can fix the issues @mnquintana pointed out in other PRs, then merge this.

[benogle]

Merged in #572