/integrate defer should be named /integrate delegate

The "/integrate defer" command name is a bit unfortunate. It is easy to confuse it with "/integrate auto", which will automatically integrate when all formal prerequisites are fulfilled; which of course is one way to defer an integration.

A better name would have been "/integrate delegate", since that is what it does -- it gives any other committer the right to integrate.

We should introduce "/integrate delegate", at least as an alias. Preferably we should also mark "/integrate defer" as deprecated.