Added a "start" option to protokoll class method

Provides a mechanism to offset the counter for the initial entry and when resetting due to date/time rollover.

__usage__

    protokoll :registry_number, :pattern => "some#####thing", start: 10000

    call01 = Call.create
    call01.registry_number
    #=> "some10001thing"

    call02 = Call.create
    call02.registry_number
    #=> "some10002thing"