create_default_expiration_notifications and introduces a new optional
configuration variable, LEMUR_SECURITY_TEAM_EMAIL_INTERVALS, to allow admins
control over the centralized email notification defaults.
* Adds additional constraints to the max notification time. With an increasing number of certificates we need to limit the max notification time to reduce the number of certificates that need to be analyzed for notification eligibility.
Mostly typos, grammar errors and inconsistent indentation in code
examples.
Some errors detected using Topy (https://github.com/intgr/topy), all
changes verified by hand.
* Renaming 'active' to 'notify' as this is clearer and more aligned to what this value is actually controlling. 'active' is now a property that depends on whether any endpoints were found to be using the certificate. Also added logic for issue #405 disallowing for a certificates' notifications to be silenced when it is actively deployed on an endpoint.
* Adding migration script to alter 'active' column.
