Apply v0.8.0-rc1 changes

[FabijanC]

Usage related changes

• Part of JSON-RPC API 0.8.0 adaptation #613
• As per JSON-RPC rc1 of v0.8.0, apply the following changes:
  • Disallow pending block ID in block and events subscription (meaning it's only left for tx status subscription)
  • Rename param: block -> block_id

Development related changes

• Expand testing of invalid block rejection to all applicable methods
  • Introduce a new test file (test_subscription_with_invalid_block)
    • Add new and existing tests here
• Add utility function for simplification of block notification assertion: receive_block (based on the recently added receive_event).
• Due to the disallowing of pending block ID in block subscription, the test subscription_to_pending_block_is_same_as_latest has become obsolete. It is replaced with assert_latest_block_is_default, since the titular fact was not tested.

Checklist:

• Checked out the contribution guidelines
• Applied formatting - ./scripts/format.sh
• No linter errors - ./scripts/clippy_check.sh
• No unused dependencies - ./scripts/check_unused_deps.sh
• No spelling errors - ./scripts/check_spelling.sh
• Performed code self-review
• Rebased to the latest commit of the target branch (or merged it into my branch)
  • Once you make the PR reviewable, please avoid force-pushing
• Updated the docs if needed - ./website/README.md
• Linked the issues resolvable by this PR - linking info
• Updated the tests if needed; all passing - execution info