- Add 'security_level' column to conference_info table in version 27 of

the database ot fix compatibility issues when migrating from release/5.2
- Allow to update participant parameters in DB
- Improve handling of organizer addition and merge into participant if
  it is also specified in the participant list
- Add test to perform migration from DB version 22 of release 5.2 to DB
  version 27 of master