7.x 4.x ticket 1072 allow option for not overriding source values

1. The market source module uses webform user to store certain values in a user's profile.

2. It derives these values either from hidden form fields, or from url query parameters that have the same keys as the hidden form fields, which then override the values in the hidden form fields.

3. At present, if there are no query parameters present when accessing a form, and the values are already present in a user's profile, the hidden form fields values get overwritten by the profile values.

4. This is not the desired outcome if the market source "persistence" option is set to "off" or "direct". If the persistence option is set to either of those values, and there are no query string values present, the user's profile should be updated with the default market source values set for that particular webform.

5. However, if persistence is set to "on", and there are no query parameters in the url, then the default market source values set for that particular webform should be ignored if there are already values present in the user profile.

I believe the above changes will effect that flow.