Conda packaging

• Updated to work with Python 3
• Added unit tests to ensure basic functionality of data2passcal
• Updated list of platform specific dependencies to be installed when installing data2passcal in dev mode (see setup.py)
• Installed and tested data2passcal against Python 2.7 and Python 3.[5,6,7,8] using tox
• Formatted Python code to conform to the PEP8 style guide
• Created conda package for data2passcal that can run on Python 2.7 and Python 3.[5,6,7,8]
• Updated .gitlab-ci.yml to run a linter and unit tests for Python 2.7 and Python 3.[5,6,7,8] in GitLab CI pipeline