Fixes for compatibility with latest Kusama runtime

Description

I discovered that the list command was returning incorrect values for rewards on Kusama and Westend, but not on Polkadot. Going down the rabbit hole investigating that, I made "some" changes on the code and I include them all in here.

Changes

Added a standard .gitignore for Python projects.
Fixed some commands on the README and made the results be with exact decimals (spoiler: as the tool returns them now).
Bumped the substrate-interface dependency to 13.3
Command list
- Accounts don't need decoding now, so we use SS58 formatted addresses for everything
- Removed HistoryDepth call, as it's not used (the depth is obtained from the config)
- Using ActiveEra instead of CurrentEra to avoid claiming rewards for an unfinished era.
- Renamed (only internally) the --unclaimedflag as args.only_unclaimed for readability.
- Using f-strings for simpler formatting of strings.
- Order results by era in DESC order.
- Fixed length of substrate.token_decimals for balances
- Fixed typos on paymemt -> payment.
Command pay
- Removed HistoryDepth call, as it's not used (the depth is obtained from the config)
- Max depth default value is now 84 (previously 82)
- Using ActiveEra instead of CurrentEra to avoid claiming rewards for an unfinished era
- Step-by-step logging
- Checking current account balance of the issuer before submitting a extrinsic, exiting if it's not enough
- Keypair generation now also reads from CLI arguments (previously was only from config). Even with this feature now enabled, I think it should be only used for development purposes. Secrets on the CLI may become visible for third parties, better use config files.
- Waiting for the batch extrinsic to be in a block before exiting.
- Logging the result of the extrinsic, with data such as its hash, the block hash, the fee or whether it was correct.
- Mapping from network to ss58_format for correct keypair generation.

Suggestion to bump version

I think these changes don't affect the usage of the tool from the user's perspective, but I would suggest to bump the version of the tool to 1.1.0.

Let me know what you think about this and the changes above, I hope you find them useful :grin:

I just saw that @arjanz has made a PR. I think his changes are also included in this PR so far, but please, take a look at both :)

stakelink / substrate-payctl