Version command

[jdknives]

Feature description

It would be generally wise to have a version command that returns the current Skywire version number. We can either add a Version file for that purpose as done in Skywallet project or add is as a variable in visor package itself. Unless there are any reasons not to go with the latter way, we should declare it in visor package as thats the way the wallet does things.

We should implement:

• CLI command for that
• hypervisor endpoint that returns version number

For now the version number can be 0.0.1 until we release mainnet.

This is a prerequisite for #129