Hide all WP nag notices while in CiviCRM

Description

Basically, while we are in CiviCRM backend we should probably hide all WordPress nag messages that appear from various extensions. It tends to get in the way and pushes all the important information on CiviCRM down.

Solution

I'm basically hiding everyhing in the #wpbody-content except #crm-container. I checked on a few designs and it's the same, and if there is some custom solution they could always force it to be shown also.

cc @bgm