inheritance-graph and call-graph don't use filenames

[rmi7]

Both the inheritance-graph and call-graph printers will create a dot file which does not include the filename. inheritance-graph creates contracts.dot, call-graph creates all_contracts.dot. This is problematic when running these slither printers an multiple files during multiple runs, as the outputted dot files always have these same names.

The fix seems to be adding call-graph and inheritance-graph in the outputted filenames, as well as the name of the file, as in:
Filename.sol.call-graph.dot and Filename.sol.inheritance-graph.dot.

Let me know if you agree or have other ideas and I will create a PR.

[rmi7]

also see #726, which is kind of related

[rmi7]

fixed in #729