Add option to exclude Summary Fields from advanced logging

[MegaphoneJon]

This patch handles the issues #40 raises in a more general fashion. Per the conversation on that ticket, this adds an option to exclude the Summary Fields table from advanced logging.

My use case is similar to @scoobird except that my client uses triggers, not cron, to update Summary Fields, so we need to exclude Summary Fields from logging altogether.

Some notes:

• I also reformatted the options at the bottom of the template to improve readability.
• sumfields_gen_data() drops and rebuilds triggers, which means that this option will be respected whenever when_to_apply_change takes effect - nice!
• There seems to be a fair bit of pre-4.7 and pre-5.0 cruft in here. Jamie, let me know if you intend to support older versions of Civi with newer versions of the extension. If not, then the next time I touch the extension I'll do some cleanup.

[jmcclelland]

Looks good Jon! Thanks for the submission. I'm about to leave town for a week so I won't have time to review it - but I will take a look when I return. I have a few PRs to go through in the queue.