Add setting fields for Adaptive Payment limitations. Start the actual implementation.

Right now all it does is track the number of times a user has pledged to a certain campaign. That needs to be used to check if an item can be added to the cart or not.
Dont't allow a pledge to be added to the cart if they have reached the set limit for purchaes-per-campaign. See #128
Hide the submission form if they have submitted too many for this calendar year. See #128
Show a note if there is a maximum pledge level that can be entered. That is about as far as i'll take it. See #128
Merge pull request #168 from Astoundify/gateway-paypal-limits

Gateway paypal limits