Simplify logging and get_paypal_order(). Removes < 2 bw compat

@thenbrent this removes the old IPN handling legacy code. Is this
something that may affect subscriptions? I believe that IPN code was
for WC < 2.0 when we used to send back a string/integer in ‘custom’
Moved paypal settings to file
Simplify get_icon() method
Use one variable for endpoint in paypal
Split up line item methods in paypal