Prevent errors on kDBConnection class change [5.3.0-B1]

If we ever going to change kDBConnection class, that is responsible for all database related interactions, then we must ensure that kDBLoadBalancer class, that allows to manage master/slave setups would also work. It's easy to forget adding a corresponding method to kDBLoadBalancer class for every kDBConnection class method.

To solve that problem I propose to create a public interface out of kDBConnection class and make both kDBConnection and kDBLoadBalancer implement it. This way PHP won't even allow to run a script if we don't add method to both classes.

What we must take care of anyway is to keep public interface up to date first.

Related Tasks

INP-1295 - Getting issue details... STATUS