New features and some bugfixes
[FEATURE] incl. page.endtime @ expirationTime #23 - thanks @xerc
[FEATURE] Added extension setting for added time #24 - thanks @EcoGabe
[FEATURE] Added minimumPageExpirationTime extension setting
[BUGFIX] Ensure CR field check works with server side validation #21
[BUGFIX] Ensure expirationTime is string when handed to hash_hmac() #24
[TASK] Use Date time aspect for current timestamp retrieval #25