pre-build libraries for Julia packages and create default git config

Build and install native dependencies of bundled Julia packages in base image. Reduces build time and space requirement for Julia packages (Dockerfile v13).

Also generating a default git config for users on first login. 

Oh. I didn't test anything beyond checking that the package installs fine with `coinor-libipopt-dev` pre-installed.
So even building into `/usr/local` may cause problems and I should let the package build everything on its own. Right?