Began scriba ID conversion

Scriba ID type is changed from 64-bit integer to 128-byte UUID
Added scriba_id_zero_init() and scriba_id_to_string() implementation
Added scriba_id_to_blob() and scriba_id_from_blob() implementation
Added new scriba id type support to the library

Library frontend, mock backend, sqlite backend now use new 128-bit
UUID as scriba id.
Serializer does not yet support the new id type.