Merge recent development to master

See merge request !24

Resolve "Behaviour Verification"

See merge request !23

No CI behaviour changes should occur as a result of this change, this
is just an upgrade that should improve maintainability.

This allows control of the version installed, and ensures greated
stability than pulling the git master.

This allows third-party converters with too generic names to be added
with more useful names.

Tests should check the response to the original request.

Replace static additional members dict with a method for programmatic
modifications.

Resolve "WP-CLI: PHP Warning about missing libraries"

See merge request !21

Merge develop into master

Closes #11 and #14

See merge request !17

Resolve "Disable plugins that are not configured for installation"

See merge request !14

This adds a new dependency to the image: jq

Closes #11

This is to acquire the the merge commit for a branch that was merged to
both develop and master seperately. No code changes should result.

Resolve "Incorrect 301 redirect to homepage when 404 would be expected"

See merge request !16