Support for empty CLI Deckfile positional argument

[buschNT]

E.g. the following commands are not working without and additional ".".

deck get
deck remove --cluster

If the positional argument "Deckfile" is not provided, getdeck could default to the CWD.

[Schille]

Makes sense 👍

[Schille]

However, the log output looks strange:
[INFO] Reading Deckfile from: .
We could also display:
[INFO] Reading Deckfile: deck.yaml or [INFO] Reading Deckfile: ./deck.yaml to make it more precise.

[buschNT]

True, I will fix this

[buschNT]

fixed via #103