Check profile_google_adsense_client_id for whitespaces and other stuff

Since you can't define it in the profile field configuration, there should be a check if the entered Adsense ID is okay.

If a user saves his ID without "ca-" or with a whitespace in front of the ID, the revenue sharing does not work. Ether a blank ad shows up, or 100% of the ad impressions come up with the site owner ID.