Add Fetchify/CraftyClicks as a provider

Fetchify is a cost-effective provider for small charities, offering special rates for organisations entitled to the PAF file without charge. These changes add Fetchify (aka CraftyClicks) as an option.

Fetchify usage is based on credits, with one credit being used for each search. This meant that partially entered postcodes were triggering a search, and most postcode lookups were therefore costing 2-3 credits (it is not possible to use the JQuery min-length criterion to limit this behaviour, due to the variable length of postcodes). The file ukpostcodelookup.js file is modified to add a regex which disables JQuery autocomplete searches until a valid postcode has been entered.