Basic System Tests for flowR

[EagleoutIce]

as discussed we want to have an additional/extra test pass which specifically tests the i/o behavior of the toplevel scripts

[EagleoutIce]

Partially as a consequence to the error in #1161.

[gigalasr]

• use https://github.com/google/zx
• repl testen
  • npm run flowr
  • :df
  • :slice
  • npm run flowr --server
  • npm run slicer