Account impersonation

[marioiordanov]

Usage related changes

Added 4 methods following JSON-RPC spec.
Closes #407

Development related changes

Added checks for impersonated accounts in DECLARE and INVOKE handler methods.
Added integration tests for account impersonation.

Checklist:

• Checked the relevant parts of development docs
• Applied formatting - ./scripts/format.sh
• No linter errors - ./scripts/clippy_check.sh
• No unused dependencies - ./scripts/check_unused_deps.sh
• Performed code self-review
• Rebased to the latest commit of the target branch (or merged it into my branch)
• Updated the docs if needed, including the TODO section
• Linked the issues which this PR resolves
• Updated the tests if needed; all passing (execution info)