Adv logging: Refine triggers for tables with datestamps

Spec from nyss#6933
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A few of the tables currently being logged contain specific columns that store a datestamp or cache-type value that is updated frequently. as a result, the row is updated in the log table more frequently than we need. we want to continue to log those tables, but refine the trigger so that we ignore updates to those particular fields.

specific tables to look at include:
log_civicrm_job
log_civicrm_group

Patch: 1st file of https://github.com/nysenate/Bluebird-CRM/commit/3039742460b681871e0e1b34a9e7fdbe6ba50d83.