PERFORMANCE - At some points we need performance increase

[steffenkux]

Current Situation

At some points, the reference implementation is too slow.

• After sign-in --> "fetching contacts..." takes a very long time if many conversations exist
• "fetching contacts" also takes >6 seconds at first login (there are no conversations!), what else ar we doing?
• Switching conversation requires some waiting

Requirements

There must be NO situation, where the user has to wait longer than 1 second.

Tasks

• [ ] What can be cached
• [ ] Is something loaded that is not needed
• [ ] Load only, what is used/visualized. Load the rest in the background.
• [ ] If no conversations are shown (in the mode for one contact only), only read what is needed for this conversation!