GitLab

Generalize levelFromUid support to support per-app, per-user,
or per-combination level assignment.  Adds a new levelFrom=none|app|user|all
syntax for specifying the desired behavior in seapp_contexts.
levelFromUid=true|false is still supported but translated to
levelFrom=app|none.

No change in existing behavior for existing seapp_contexts configurations.

Change-Id: I0e9c18ecf3113fa7079d2101899c92a241ef80a0
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>