Add machine-friendly output for commands

[spyrkob]

Add --plain or --json flag to the commands.

When the flag is used, the output should be minimal (e.g. no progress updates) and easy to parse in scripts, etc.

For instance the output of calling prospero install --json --profile wildfly --dir wfly would be:

{
"status": "OK",
"operation": "install"
}

or in case of an error:

{
"status": "ERROR",
"operation": "install",
"error_code": "PR01234"
"msg": "Description of the error"
}

[TODO] define the format of messages for all commands