docker: python bytecode cache

• Adds docker build step that precompiles all python files. This improves Invnenio start up and test time. It is required to do this during the build phase because the Invenio user does not have write access to the python files.

• Adds *.pyo files to .dockerignore and .gitignore.

• Changes docker volumes in dev setup so that the Docker process has the ability to write pyhton bytecode files. Please note that updates after the build phase invalidate the bytecode files and a rebuild needs to be done by the root user.

Signed-off-by: Marco Neumann <marco@crepererum.net>