#213 Do not update Exchange field Modified if only GCSM fields changed

[LairdB]

GCSM creates fields g/con/[googleaccount]/id and g/con/[googleaccount]/up in the Exchange contact record, and updates them on establishing a g-relationship or on any change (whether material or not).

Initial relationship establishment, and trivial or sync-related changes, should not update the Modified field, otherwise it becomes useless in practice.