This patch enables catching HttpError exception raised
by PSA because of any issue caused at client/server.
Further it redirects user to login page with a
message about the error.
LEARNER-4344
PSA was monolothic, now split, with new features, like
a DB-backed partial pipeline. FB OAuth2 version also upped.
Partial pipelines don't get cleared except when necessary.
They persist for special cases like change of browser while
still mid-pipeline (i.e. email validation step).
Refactor, cleanup, and update of a lot of small things as well.
PLEASE NOTE the new `social_auth_partial` table.
