Improve API error messages

[eschwartz]

Using dce-cli v0.2.0

API error are not super user friendly:

eg.

~/$ ./dce-cli accounts list
err:  [GET /accounts][403] getAccountsForbidden ~/$ 

Proposing to:

• Use human-readable error messages (eg, "You do you not have access to get account", or whatever)
• Add a newline character to the end of the message, so the CLI prompt starts on a new line

[eschwartz]

Besides human-readable error messages, it would be nice if we have an optional way to see the entire API error response, like with a verbose log level configured, or in a log file somewhere