Improve signal handling and refactor watchdog

Remove orphaned childs detection as it should not occur in normal operation
and will be caught by the (not yet implemented) reap_at functionality.

Reload signal now reloads notify and watchdog configuration, fixes #40
PKCS7 Refactoring, new API call validate_certificate and extension of X509 auth handler

Remove get_subject and is_not_self_signed from pkcs7 helper token (openca helper)
Refactor pkcs7_get_chain to deliver the funtionality from get_subject and pkcs7_get_end_entity
and work without a predetermined signer subject.

Deliver a cryptographic validation of a certificate by new api call validate_certificate.

Rebuild x509 based authentication to verify the chain based ont this method, allows usage of
external certificates (need to import only the root certificate)
Fix hickup with XSRF code
Refactor CSR/CRR approval with signature
Refactor of X509 Client authentication handler