Scaling - Remove dependency on environment variables

[Snehaost]

Problem: Environment variables are a hard dependency. Due to which for having multiple instances of "OpenST-Payments" connecting to different AWS DynamoDB instances OR different Memcache instances is impossible. This is because the connection parameters for these external services, presently come from environment variables. This makes scaling to multiple AWS DynamoDB or Memcache or GETH utility chains impossible.

Solution : Remove dependency on environment variables. How do we do that - We shall now pass the configuration information of "OpenST-Payments" service via a parameter in its constructor. This will give us the flexibility of using one AWS DynamoDB endpoint in one instance and other endpoint in another instance of OpenST Payments.

This will enable us to instantiate multiple instances of "OpenST-Payments" based on an applications infrastructure requirements.