Add method getUserByUsername(...).

From Java to Kotlin. Also delete the SortDirection attribute (avoid conditionals checks).

Fixes message history randomly missing from room

Updating presence status to offline instead of removing the user from Realm, whenever server sends a removed message for a user

Spotlight changes.

Removed keep-alive task and fixed the login and sign-up

 Spotlight: search for users.
Closes #321 

Merge fix on Avatar into develop

Avoid Realm queries for messages with null users

Fix on building the default avatar