Introduce the SecurityAgent, which assesses and enforces system security

Description

Adds a Security Agent to the system, which performs regular security checks:

• The user running AuTA may not be root
• The authentication database should not be world-accessible (any of rwx)
• The authentication database should not be executable by anyone
• The default privileged user's passwords should be changed

Changes

None.

Additions

• The SecurityAgent service
• The system now performs an initial security check before it allows workers to connect
• Repeated checks happen every 30 minutes
• A hasUser method for the database which is slightly faster than full user queries

Test and Review

Closes #128 (closed)

To be filled in by the reviewers

• All of the methods are commented to expectation

• The methods are tested to satisfaction

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date

• All nullable parameters are marked as such