Python Distribution

[alecandido]

Follow up of #176

• [ ] prepare CI for release
• [ ] add dependency on this new package in the pineappl Python package

The overall idea is to build everything in the CI, and supplement the current default PineAPPL package with CLI installation.

This partly address #129, since a quick binary installation will be available through pip (but it does not solve the problem of the C API).

[cschwan]

Done in #266.