Create Beacon Network CLI

[mcupak]

Implement a CLI talking to the Beacon Network API.

Links:

• Beacon Network API
• Beacon Network API docs (we have interactive Swagger-based docs as well, please contact mcupak for access)

Requirements:

• The client should not be interactive, for easy automation. In other words, a single execution of the client should perform a single operation and exit, with all the necessary parameters passed as arguments.
• Consistent API cleanly mapped to the REST API, e.g. cli beacons list --beacon test.
• Prefer arguments over configuration through static files (e.g. properties files). The host should be configurable as well and default to https://beacon-network.org/api/.
• Use a library for argument parsing (e.g. JCommander or Args4j).
• CLI should be runnable both as a self-contained jar file incl. all its dependencies and via Maven exec plugin.
• Beacon Network provides JSON and XML APIs. The client should utilize the JSON API and provide results in JSON.
• Java client library should be used (Create Java API library beacon-network-client#1).
• Standard Unix conventions for return values (error indication) should be used.
• Proper help should be included (global as well as per-operation, if needed).
• Unit tests.
• Documentation (at least README.md).