Fix import loop issue
The following discussion from !143 should be addressed:
- @moul started a [discussion](https://git.duniter.org/clients/python/silkaj/-/merge_requests/143#note_23695): (+1 comment)
> Is there anything that can be done for this import loop issue?
> Did you try to understand the importation process order?
> I haven't check in details, but this is usually due to a wrong architectural design.
---
- [x] Get rid of `convert_time()`, and generalize `pendulum` usage
- [x] Remove following weird imports:
```bash
grep -rnA1 "had to import" silkaj
silkaj/money.py:27:# had to import from wot to avoid loop dependencies
silkaj/money.py-28-from silkaj.wot import check_public_key
--
silkaj/auth.py:26:# had to import pubkey_with_checksum from wot to avoid loop dependency.
silkaj/auth.py-27-from silkaj.wot import pubkey_with_checksum
--
silkaj/wot.py-29-from silkaj.tui import convert_time, pubkey_with_checksum
```
issue