Add dependencies for PlantUML and Graphviz and update Mermaid version

[wuan]

This PR adds support for PlantUML and Graphviz based diagrams through

[graphviz]
....
digraph G {
  Hello->World
}
....

or

[plantuml, target=diagram-classes, format=png]
....
foo -> bar : preload
bar -> baz : execute
baz -> foo : return
....

In addition the Mermaid dependency has been updated and we are using the official Docker images as a base to reduce build time.