Contacts: app skeleton and contact folders

[kulmann]

Initial Checklist

• I understand this is a user story and questions should be posted in the Community Discussions
• I searched issues and couldn’t find anything (or linked relevant results below)

User Story

• As a user, I want to see the list of contacts in my selected account so that I know if I have details about a certain person.

User Value

Contacts MVP

Acceptance Criteria

• new app "contacts" is available in the app switcher if groupware is enabled
• set up transifex config
• left sidebar shows account switcher at the bottom (same as in the mails app, see Move groupware account switcher and store into shared package #1973 )
• main view renders empty for now
• upon account selection the list of contact folders for the selected account gets loaded
• left sidebar shows contact folders at the top, but without any possibility to interact with it