Sync schema.rb and add pending migrations

[MrSerth]

There are two issues with the schema.rb we should resolve:

1. The schema is currently based on the production setup. However, running rake db:migrate:reset will cause another schema. This should be fixed (maybe by fixing our production setup and adding further migrations, e.g., regarding varchar(255) vs varchar).
2. With commit e210795, some changes were made to the schema that do not necessarily have a corresponding migration. Some parts were just caused by a different column order (based on the production schema), but it also introduced the code harbor_links.user_type column. This was caused by the previous migration AddUserToCodeHarborLink amended in commit 2118e61 without updating the schema correspondingly.