Implement quickfix for MANY_CLASSES_IN_SUPERTYPE_LIST

Revision of https://github.com/JetBrains/kotlin/pull/224 (is it possible to reopen the old pull request instead of sending a new one? I could not find it)

What has changed since last time?

As advised, the RemoveSupertypeFix now operates with JetDelegationSpecifier (encompassing both JetDelegatorToSuperCall, JetDelegatorToSuperClass).

Two new tests are added to ensure that examples pointed out by @goodwinnk are fixed correctly.