Web client: E2EE Setup

Goal:

Prepare the postbox Web client project to use the E2EE. The application should be able to send and receive an encrypted message.

Acceptance Criteria:

• There is a functionality/ implementation that:
  1. logs into a homeserver with a demo account
  2. sets up a sync loop and local storage
  3. sets up the crypto store
  4. sends and receives an encrypted test message

Notes/ resources:

• iOS reference ticket: #113 (closed)
• Blocked by #170
• Reference ticket (technical breakthrough): #15
• Requirements uIDs: Zapuk_18; Zapuk_80; Zapuk_104; Zapuk_115; Zapuk_117; Zapuk_128