Show server version when running Spg

[dvallin]

Is your feature request related to a problem? Please describe.
When running spg it might be running against a different version of Spacegun. The user should at least be informed about that.

Describe the solution you'd like
Add a server version endpoint. If the server can be reached the fetch the version on ANY command and compare to the local version. If command is version or help also show the server version and a warning on version mismatch.
For any other command: print a warning before doing the command on version mismatch.

Describe alternatives you've considered
Just looking at the server version on the servers webpage does not seem to work as good as a direct CLI integration.