tornevalls-resurs-bank-payment-gateway-for-woocommerce

RWC-234
Fix #32.

Changed the way we test credentials to make sure credential problems are visible.

Callback controller now reports back current tab, so that alerts can be avoided.
On errors, checker reports back to credential elements if they exist.
Moved setRbwcGenericError to global script to make sure stuff are logged in console.
Created functions to get and set credential errors via options.
Embedded first callback cleanup to check if credentials are invalid.
Refreshing callbacks is now only alerting when credentials are valid.