Lowest and highest price options

This allows price keys not to be ordered like [0,1,2...] but also can be
random ids if needed
Merge branch 'fix/price-options' of github.com:somewebmedia/Easy-Digital-Downloads into
somewebmedia-fix/price-options
Merge branch 'somewebmedia-fix/price-options'
Formatting and brackets clean up for edd_get_lowest_price_option() and edd_get_highest_price_option()
Merge branch 'master' of github.com:easydigitaldownloads/Easy-Digital-Downloads