[test] #236: add tests for tx confirmation, mock functions:

* add tests for display_pubkey(), display_amount() and transaction_confirmation() in tests/test_unit_tx.py.
* patch async functions.
* create the patched.py module containing patched/mocked functions.
* modify silkaj/tx.py to match patch requirements:
  * `from silkaj.wot import is_member` -> `from silkaj import wot`
  * `await is_member()` -> `await wot.is_member()`