Setup simple ci

Simple CI using shared runners and an anaconda image (2 resp 3). Installs ROOT (6) and root_pandas in the root env, then installs analysis-tools. After the installation, pytest is run with coverage report. Estimated elapsed time: 7-8 min

It is quite simple and can surely be improved but it is especially useful to track the python 2/3 compatibility of the project.

Currently fails as dependencies in setup.py contains an illegal statement, should work after merge of fix_deps and py23