Introduce some breaking changes for 0.7.0

[FabijanC]

Usage related changes

• Close Implicitly calculate maxFee #164
• Close Fix return type of StarknetContract.decodeEvents #165
• Close Make --account-contract of hardhat starknet-verify a flag rather than a param #173

Development related changes

• There probably are some, but I don't remember them because it's been some time

Checklist:

• Formatted the code
• No linter errors + tried to avoid introducing linter warnings
• Performed a self-review of the code
• Rebased to the last commit of the target branch (or merged it into my branch)
• Documented the changes
• Updated the test directory (with a test case consisting of network.json, hardhat.config.ts, check.sh)
• Linked issues which this PR resolves - INCLUDING those already linked in PRs to branch release-0.7.0
• Created a PR to the plugin branch of starknet-hardhat-example:
• All tests are passing (for external contributors who don't have access to the CI/CD pipeline)
• Tests are marked as passing but are actually failing, this should be fixed!