Extend test/README.md
Update test/README.md

* Some info on automated tests with Travis
* Dependencies for the manual tests
Add `rehash` in `runtest`
Rewrite README completely

I improved the structure of the text by dividing everything into sections.
Old dependencies have been updated to more relevant versions.
Some sections that are documented elsewhere, e.g. `signalflow` in the wiki,
have been removed in favor of a link.
Merge branch 'fixReadme' into develop