Add Update Plugins button

[Botan626]

Checklist

• [X] I read and understood ASF-ui's Contributing Guidelines
• [X] I also read FAQ
• [X] My idea doesn't duplicate existing ASF-ui functionality described on the wiki
• [X] I believe that my idea falls into ASF-ui's scope and should be offered as part of ASF-ui built-in functionality
• [X] This is not ASF suggestion

Should be equivalent of updateplugins command without args.

Sketches are important, and I managed to make one, though I've not read a single book, recommended by professor.