Add support for --version/-v

Implemented according common practice with argparse.

$ poetry run expliot -h
usage: expliot [-h] [-v] [cmd] ...

EXPLIoT - Internet Of Things Security Testing and Exploitation Framework Command Line Interface.
[...]
options:
  -h, --help     show this help message and exit
  -v, --version  show program's version number and exit

$ poetry run expliot --version
0.10.0

Also, uses importlib.metadata to get the version which makes the tracking in constants.py obsolete.

Fixes #74 (closed)