Get rid of the Context

[jpcenteno]

• The design of EthClient is built around the reading and writing of the Context module.

Problems that we encountered so far:

• The Context module acts as a mutable global variable.
• Editing the context in one livebook notebook modifies the context for the other as they share the same runtime.
• What if we want to work with multiple accounts or multiple contracts?

Proposed solution

Instead of having functions like EthClient.deploy/2 using the Context state as an implicit input, have them receive a %Client{} structure:

EthClient.deploy(client, bin, abi)

Where the %Client{} structure contains the configuration needed for a specific blockchain network.