Fixes CfP-Start-Date
Fixes CfP-Start-Date

Currently the start-date will be reset to the current date on every call
to the API when no startdate is given.

This commit will stop that behaviour by presetting the CfP-Startdate to
timestamp "0".

joindin/callingallpapers-api,joindin/callingallpapers-api,heiglandreas/callingallpapers-api,heiglandreas/callingallpapers-api,heiglandreas/callingallpapers-api