Add defense-in-depth: seccomp & apparmor

[deeplow]

Consider adding defense-in-depth mechanisms limiting the scope of what a compromised dangerzone & associated programs can do on the system.

Strategies to consider:

• apparmor
• seccomp

Related:

• Container hardening #52 - seccomp mentioned but not implemented

[deeplow]

This should be added only after setting up a set of automated tests both to help generate the profiles and to guarantee we caught most regular usage.

[eloquence]

Tentatively added to 0.4.0 milestone, but we'll need to decide initial scope (e.g., AppArmor only?).

[apyrgio]

Closing this issue in favor of #225 (seccomp) and #227 (AppArmor), which are part of the larger #221 (defense in depth) issue.