Set of tests to the `decline_voting_rights` and `proxy` operation.

This MR:

1. Set of tests to the decline_voting_rights operation,
2. Tests for proxy operation,
3. Test showing problem with decline_voting_rights on hf 27. Tests before the fix are placed in the directory functional/python_tests/hf28_tests/tests_showing_problems_on_hardfork_27.py. Represent real problems to be solved. After the fix, find the test corresponding to the name (without the _on_hf_27 suffix) and remove the @pytest.mark.skip marker

Corresponding issue: #441 (closed)

Should passed on HF27: test_decline_voting_rights_more_than_once_on_hf_27

Should passed on HF28: test_decline_voting_rights_more_than_once