Add history table for course access rule changes.
Provide test utility for simulating restricted access.
Provide `redirect_if_blocked` method for integration with other
parts of the system (will be used for blocking enrollment).
Add info-level logging explaining when and why users are blocked.
The previous version of this migration incorrectly handled
disabled configuration. When configuration is disabled,
the embargoed country field was the empty string; calling
str.split(",") produced a list with a single empty list entry,
which is not a valid country code.
Allows specification of countries to embargo, what course(s) should
apply embargo restrictions, and whitelist/blacklist capability for
specific individual IP addresses.
Adds configurable middleware in common/djangoapps/embargo that
allows specific courses to comply with US Export regulations by
embargoing students from specific countries, whilst simultaneously
allowing other courses to be freely open to all.
