Add --version support

[jclapis]

This adds --version support to the CLI, PBS, and Signer binaries. For example:

$ commit-boost-pbs --version
Commit-Boost PBS Service v0.9.2

Now people can check the version of their binaries without needing a full proper configuration to start and stop the services. This should close #375.

As a side-note, I left each config as an independent struct per binary. They're empty right now, but they use clap so we can easily add more stuff to them later when we fully CLI-ify each one individually.