Refactor tracing code in the flow-graph library

Instead of big select cases, call the right functions.
This also moves the filtering to the flow-graph library, which
was adapted from the dfmc-optimization library.

DFMC flow-graph now exports all the tracing functionality needed.
Refactor tracing in the optimization library

By simply using the provided interface from the flow-graph library
Refactor tracing support from management

By simply removing all of the stuff, apart from the
``init-flow-graph`` call, which clears the *lambda-string-table*
(A hack to name top-level-initializers uniquely)
Remove the visualization keyword argument
Refactor tracing support, remove it from the environment

Removing visualization features from the command-line compiler.
This was a bad idea in the first place, since it introduced dependencies
on the network library, and a serialization library.

The API for tracing is provided by the dfmc-flow-graph library.
Remove serialization submodule
updated release notes
point to a user
Merge pull request #669 from hannesm/more-fixes

Rework tracing support