Extrinsics follow ups

[ascjones]

Follow ups to #79. In no particular order, should be promoted to their own issues.

• Add support for remove_code extrinsic.
• Gas estimation: auto dry run first to use estimated gas as a value for the gas limit when running actual call.
• Add flag --wait-for-finalization. so that success/events are not displayed until the block is finalized
• Denominated units for Balances e.g. 100CAN, 1MCAN, instead of e.g. 10000000000000000000000000000
• Signing: safer alternatives for value bearing chains than providing secret key on the command line. Possibly allow using encrypted file with private key, or integrating with external signers somehow.
• Dynamic DispatchError::Module errors, so that error details are displayed correctly across different chains Dynamic DispatchError::Module details paritytech/subxt#443
• Bitvec encoding/decoding
• Improve error message when failing to encode contract message arg e40dc80
• Set up CI with substrate-contracts-node and unignore integration test: https://github.com/paritytech/cargo-contract/blob/60f65a2863be1266882bdd81861d836baeb06724/src/cmd/extrinsics/integration_tests.rs#L124 Fix extrinsics integration tests #518

[ascjones]

Extracted all to separate issues, or PRs already in progress