Change from using 'cypher_type' to 'mode' in API and code base.

The term 'mode' is better aligned with the cypher community than
'cypher_type' is. Therefore, it would be less confusing to change
the name of this attribute prior to the M3 feature freeze.

Change-Id: Ibf99bd730e9a3ff7bd1f49f4252cc860a60e9295