DAV: Single-type calendar and tasks folders

Summary:

• Don't store tasks and events in the same folder, set new folder supported-calendar-component-set appropriately
• Make single request on folder creation. Before it was MKCOL + PROPPATCH, now it's MKCOL

Test Plan: Create Tasks folder, check it does not appear in Calendar, and vice-versa

Reviewers: Roundcube Developers, mollekopf

Reviewed By: Roundcube Developers, mollekopf

Subscribers: Roundcube Developers

Differential Revision: https://git.kolab.org/D4656