Add Conda Installation Support

[bhgomes]

It would be extremely beneficial for users of the Conda environment/build system to be able to install reana-client and reana-cluster through Conda. There are several options for doing this:

1. Adding reana-client and reana-cluster as conda-forge feedstocks.
2. Creating a reana channel on Anaconda Cloud to host reana-* packages.

Using 1 has the benefit that users can install very easily because most people have conda-forge setup.
Using 2 has the benefit that it is easier for reana devs to add packages/projects to Anaconda Cloud than to conda-forge and you would not be bound to conda-forge conventions.

Either way, I think it would be extremely beneficial to have this setup, especially since many projects in the scientific-python community use conda.

[tiborsimko]

Thanks for the suggestion, yes, it would be definitely useful, especially for reana-client that is used by the scientists. The reana-cluster is used by the cluster administrators/developers only, so having the package on PyPI is probably enough... Although it wouldn't hurt to expose both.