Replace chalk

[rtfeldman]

I want to replace the chalk dependency on the JS side with console-print on the Elm side. That will make the code nicer to work with, and should be a performance optimization; instead of encoding more data to send to JS, we can get by sending a plain string to JS instead.

A prerequisite is doing the terminal detection up front (on the JS side), and then telling the Elm code to either render colored or monochrome console output. (Note that we also need to do terminal detection up front for #169 so we can tell whether to output a progress bar.)

There's also no reason end users need to know about the chalk dependency, so I'd like to take it out of the CLI args. Current --report docs look like this:

#### `--report`

Specify which reporter to use for reporting your test results. Valid options are:

- `chalk` (default): pretty, human readable formatted output
- `json`: every event will be written to stdout as a json-encoded object
- `junit`: junit-compatible xml will be written to stdout

I'd like to replace them with this:

#### `--report`

Specify which reporter to use for reporting your test results. Valid options are:

- `console` (default): console output, with colors only when color support is detected
- `json`: every event will be written to stdout as a json-encoded object
- `junit`: junit-compatible xml will be written to stdout