The shell executor is started in an healthy environment already;
the commands are needed mainly for the docker runner.

The runner is selected via a tag. No need to specify a customized port.

This reverts commit a0a8064d.
It is actually not necessary to use the base64 encoding anymore,
because the reason for which the variable was not passed to the
runner was the fact that the branch was not protected.

This is due to issue in difficulties in getting the right parms and keys to lektor

This was done to avoid running into [this
issue](https://github.com/vuejs/vue-cli/issues/3407)

Now every image attachment will be displayed on page top, just before
the actual content. This is enabled by default in the page model

Previous node sampling was a heuristic that may loop infinitely.
Now using proper CDF sampling. Corrected labels, we compute a MST
not a Steiner tree.