- Update GitLab to 12.3.4

- Update update.py to cope with the new upstream repository structure

- Refactor gitlab-shell to use buildGoPackage and bundlerEnv for
  dependencies

- Refactor gitlab-workhorse to use buildGoPackage for dependencies

- Make update.py able to update gitlab-shell and gitlab-workhorse
  dependencies

- Various fixes necessary for update to work

Split the remove-hardcoded-locations patch into two separate patches,
one for the ruby package and one for the go package. This is clearer
and results in fewer rebuilds.

Instead of extracting prebuilt assets from the debian build, build
them from the source. This should give faster package updates and
reduces the amount of data needed to be downloaded by more than 500MB.

GitLab recently restructured their repos; whereas previously they had
one gitlab-ce and one gitlab-ee repo, they're now one and the
same. All proprietary components are put into the ee subdirectory -
removing it gives us the foss / community version of GitLab. For more
info, see
https://about.gitlab.com/2019/02/21/merging-ce-and-ee-codebases/

This gives us the opportunity to simplify things quite a bit, since we
don't have to keep track of two separate versions of either the base
data or rubyEnv.

gitlab: 12.1.6 -> 12.3.5, bundler: 1.17.2 -> 1.17.3