[feat] #262: Add 'verify' command to check blocks’ signatures

- Based on DuniterPy 0.56.0 which implements block signature
  verification
- #183: Click progress bar
- Handle BMA anti-spam protection whith an exception
- Possibility to pass starting and ending block numbers to verify them
- Default to 0,0(head) for the full blockchain
- Get rid of the client singleton, in order to have full control over it