/epoch command

[callmephilip]

Is your feature request related to a problem? Please describe.
Discord users should be able to get information regarding current epoch via /epoch command

Describe the solution you'd like
Extend Commander bot to support /epoch command

Additional context
From previous discussions:

I'd like us to simplify this and show:

- when the current epoch starts
- when the current epoch ends
- pretty version as the title: ends in… 
- emissions amount in tokens
- emissions amount in $-value
- rebase amount in tokens
- rebase amount in $-value