Provide CLI Client for GRPC

[uweschaefer]

From @uweschaefer on 2018-10-19 14:45:26 +0000 UTC

Is your feature request related to a problem? Please describe.
As a User, i'd like to play with a remote Server (peek into it, subscribe, publish ...) quickly.
It'd be nice, if we'd provide a generic client for that

Describe the solution you'd like
Executable JAR, that provides most of the GRPC API Features and makes them accessible from the command line.

Additional context
Based on Mercateo/factcast#148

Copied from original issue: Mercateo/factcast#152