GET_PROTOCOL_PARAMETERS for retrieving latest protocol params

[slowbackspace]

Currently the clients can't build a transaction just by using the data provided by wslink - for setting TTL the client needs to know current slot, also various protocol params are needed during tx builder setup (pool_deposit, key_deposit, ,coins_per_utxo_byte, max_value_size, min_fee_a, min_fee_b). We could exposes needed information by implementing new command for retrieving latest protocol params.

Note: After implementing this we could deprecate ESTIMATE_FEE msg since the information would be included in the new msg.

[iccicci]

Done with #272