Improvements to the deposit system

[oscarguindzberg]

• Define fair deposits required fo each operation: challenge, each particular query, each particular response to query. Today: 1 wei for everything
• Deposit should cover what I am forcing the counterparty to spend + a reward to the counterparty. Measure how much gas is required for each operation and harcode constants with those values.
• Define a harcoded value for gas price