Add option to allow members of whitelisted organizations to whitelist users/trigger PR tests

This adds a config option to allow members of whitelisted organizations to effectively behave like they were entered into the admin list, which is more practical for organizations with many members.

We are using this at the Mono project since a few days and it seems to work fine :)
The global config will not have this option unless you add it to the global.jelly file.  If you don't want to configure it globally just remove the option from this section, and remove the default on config.jelly#34.  Otherwise just copy 33-35 from config.jelly into global.jelly where you want the option to appear.  I am not sure how this affects the local config, I think it makes it so that the local config will always be set to the global when you go to configure the job and would need to be corrected every time you edit the config for a job if the setting doesn't match global.