Try to fix publish step.

- modify md_convert to use more robust way to make local installation of
"grip", tool for conversion MD files to HTML
- modify publish rules to get correct branch info to copy from correct
build-* directory. Note, that Jenkins do not follow symbolic link, so
flow123d/build_tree can not be used.
Merge branch '1.8.0_master' of github.com:flow123d/flow123d into 1.8.0_master