Add support for blockdiag actdiag nwdiag packetdiag rackdiag seqdiag

[priiduonu]

No description provided.

[tarleb]

Thank you for the PR, and apologies for the late reply, I had to let my open source involvement rest for a while.

I'm still a bit on the fence about this PR. My rule-of-thumb on what code to include here is whether I'd be willing to maintain the code myself, and I'm not sure in this case. My preferred solution would be to have this in a separate repository, with instructions on how to use it as an engine via the package configuration option.