Missing error handling in checkout

[syntaxerror]

The error handling in the checkout kind of sucks... ;)

T.ex. if there is some kind of mail issues the order will be placed when the customer clicks the confirm button, but there is nothing informing the customer about it, the button just loads before it becomes available to click again. The customer can therefore place the order several times, and even believe the order wasn't placed, and thus go order from someone else whit a working cart instead ...

To test, change to SMTP sending of mail and fill in non working mail credentials, activate Bank Transfer or COD, and go to checkout. Click confirm button ...

This also applies to other issues, like but not limited to, cURL-connection issues.

Ref #482

[denisdulici]

A complete rewrite using try catch is required.