Change Jenkins to use a single consistent data-binding field.

See also: https://github.com/stapler/stapler/pull/39

This commit includes several changes to accommodate the aforementioned change to Stapler (moving away from 'stapler-class'), as well as to make Jenkins consistently use this same JSON field (moving away from 'kind').


NOTE: Stapler will continue to accept 'stapler-class' for backwards compatibility, and similarly this will continue to pass 'stapler-class' for plugins that have keyed off of it.
I'd rather avoid dynamically patching the requests, as it leads to counter-intuitive behavior, and that leads to developer frustration...

The idea was to make Jenkins submit both, get folks to migrate (send mail, submit PRs), and then remove the old way after some suitable deprecation window (and more mail).

FWIW, in my experience Jenkins is already submitting this twice in many/most cases today due to "kind".  There is also a lot of other garbage in the form submissions, so this can't be too concerning...?


That said, if there is official process here, I'm happy to follow that.  

thanks,
-M