Simplify Raiden Smart Contract version bump

[eorituz]

Problem

Right now every new version of the Raiden Smart Contracts require and update of the requirements.txt file as well as writing a new class in raiden-installer/tokens.py.

Todo

• Find a way to "simplify" the upgrading to a new raiden smart contract version.
• Refactor the whole Token.py

[eorituz]

How to update the raiden smart contracts right now

There are several things that have to be done manually atm to update to a newer version of the raiden smart contracts. (This is necessary because the raiden client, the raiden service bundle and the raiden smart contracts have to be compatible).

• Update the raiden version in the requirements and reinstall the requirements afterwards.
• Add a new Token class like this one
  --> Note: The "RDN" Token is called Service Token (SVT) on all testnets!
• Add new Token class to the "list of tokens"