Domain/Selector/KeyFile should not be mandatory in verifying mode

[glts]

OpenARC does not start without parameters Domain/Selector/KeyFile set.

In verifying mode (Mode v) these parameters are unused and should not prevent OpenARC from starting.

Compare with OpenDKIM, which can be started without Domain/Selector/KeyFile in verifying mode.

[Swallowtail23]

Second this. I'm currently running OpenARC in 'v' mode only, and had to dummy up the three entries noted to get it to start, despite no need for them in 'v' mode.

[minfrin]

Fixed in #159