[Feature]: Rewrite contact list using SwiftUI

[tmolitor-stud-tu]

Precondition

• I understood that this template is only for feature requests and not for bug reports

Cross-checked related issues?

• I have cross-checked this overview Overview: Tasks and Issues #322 as well as filtered for related labels https://github.com/monal-im/Monal/labels

Describe your feature

• Rewrite ContactsViewController.m using SwiftUI and our new ContactEntry SwiftUI view
• Add support for roster groups as tags to ContactEntry, will fix Support for client roster organization based on server-side Roster Groups (see RFC 6121, 2.1.2.6. Group Element) #121

[tmolitor-stud-tu]

@matthewrfennell despite stating otherwise in the roster groups issue, we should add support for setting/changing roster groups, too...could be a simple button beneath the list of roster groups in the contact details leading to a text entry box and a "save/cancel" button...possibly using RichAlert to display that edit window.