Express Checkout button override. (fixes #6)
Minor updates
Merge remote-tracking branch 'origin/quick_check_out' into dev
- comments out 'checkout_with_pp_button' and 'hide_checkout_button' setting
- add new setting 'show_on_product_page'
 (fixes #6)
- check show_on_product_page before show it on product page
- default to paypal image button
 (fixes #6)
Merge remote-tracking branch 'origin/quick_check_out' into dev
Updates option labels