Cascade delete BilingAgreement from PaypalAccount
Merge pull request #832 from sharetribe/billagr-dependentdestroy

Cascade delete BilingAgreement from PaypalAccount
Use community's favicon in error pages, not ST icon
Remove Sharetribe from error page title
Use layouts as they should be used
Current community and favicon
Take new error page layout in use
Remove airbrake from feedback mail
Improve Airbrake notification

- Remove the extra "empty" notification
Minor edit to English copy text