Normalize way for projects to handle dependencies

[alerque]

See previously #55.

Some projects may have extra dependencies. Right now we offer a hook where they can check for them and utility functions to look for example fonts, but no really way to satisfy them. For the sake of CI builds there should be some normalized way of specifying packages that need to be installed into the Docker container before runs. This is in addition to checking for them for the sake of local runs.