Enhancement to the Repository.prototype.continueRebase method which allows a RebaseOptions to be passed in. This achieves parity with Repository.prototype.rebaseBranches.

Also introduces a breaking change from the error handling pattern introduced to continueRebase in BREAKING: Convert sync methods to async methods #1348. Previously, all errors which occurred in the middle of a continueRebase operation would be swallowed. However, the introduction of signingCb as a field on RebaseOptions shed light on legitimate use cases where continueRebase should throw. My solution was to swallow the EAPPLIED error (specifically mentioned in the review of BREAKING: Convert sync methods to async methods #1348) and throw all others.