Unify means of specifying environment to --env=<environment>

*If omitted & param is optional, defaults to 'dev'
*Supports arbitrary environment --env=foobar
*Deprecates support for `fhc restart appId live` or `fhc restart appId --live` - still supported but prints a warning

There'll be more work for FHC when things with dev/live specific endpoints (hosts `developmentHost`, env's `devValue`) are updated - deemed not in scope here. 
What environment is targeted if none is specified? Should this param actually be optional? If so, the description should be updated to say what the default is.