[#64605932]Incremental commit. Please do not base any external work off of this commit.
Redis session persistence

This change adds persistence of sessions to Redis.  In addition to the
obvious save() method, all of the other methods that touch Redis (e.g.
load(), keys(), getSize(), clear()) have been implemented as well.

[#64605932]
Merge 64605932-persist-session to master

[Completes #64605932]