Improve env var setting upon new deployment

[lasse16]

Currently Dotter offers no way of setting environment variables upon deployment.
I worked around that by sourcing the rendered template of my .dotter/pre_deploy.sh hook.

This is however a hacky way. It generates several annoyances with subshells, returning processes, inherited environment variables.
Currently upon deployment via dotter deploy, there are no environment variables set.
I wrote a custom wrapper script, setup_full.sh, which sources the rendered template in .dotter/cache/.dotter/pre_deploy.sh.

Two issues are mentioning the problem, this and this. They are however not implemented yet.

Keep up to date with those issues and think of a better solution.