API: Fix documentation for ApiBase::require*OneParameter

The existing doc blocks for all three of these functions is entirely
wrong.
* ApiBase::requireOnlyOneParameter
* ApiBase::requireMaxOneParameter
* ApiBase::requireAtLeastOneParameter

Change-Id: Id0dd86be3cbfa813a43f918c7d780c7ee2afc09e
Require one of page id or page title as params to ApiRollback

Also made the code flow easier to understand by moving
calls to ApiBase::extractRequestParams up in the stack.

Change-Id: I346c6ae4fc0b48c5a794c3d621018baf9bde6b9e
Follows-up: I9c4e4fa
Merge "API: Fix documentation for ApiBase::require*OneParameter"