Fix crash in maindb tester, and relax wait time in group chat suites because with --parallel mode there were sometimes exceeded.

This reverts commit 1d0495f8.

  - return nullptr if conference factory uri is not set
  - Address object is now more robust
  - remove custom SharedFromThis object
  - CoreAccessor throw exception if core is destroyed
  - Core must be created with a static method
  - Partial fetch of chat message
  - ...