Add support for user-configuration language tag specification. (#1038)

Adds a new top-level configuration key called "language":

```yaml
wtf:
  langauge: "ja-JP"
```

Users can now define which BCP 47 language tag to use to format any
text or numbers that currently support localization. Defaults to
"en-CA".

Acceptible values: any BCP 47 language tag recognized by the Go
"language" package.

Good luck to you figuring out what that cannonical list is. After a
morning of trying to suss it out, I have no idea.

Signed-off-by: Chris Cummer <chriscummer@me.com>

modules/twitch/widget.go

@@ -105,12 +105,14 @@ func (widget *Widget) content() (string, string, bool) {
 	}
 	var str string
 
+	locPrinter, _ := widget.settings.LocalizedPrinter()
+
 	for idx, stream := range widget.topStreams {
 		row := fmt.Sprintf(
 			"[%s]%2d. [red]%s [white]%s",
 			widget.RowColor(idx),
 			idx+1,
-			utils.PrettyNumber(float64(stream.ViewerCount)),
+			utils.PrettyNumber(locPrinter, float64(stream.ViewerCount)),
 			stream.Streamer,
 		)
 		str += utils.HighlightableHelper(widget.View, row, idx, len(stream.Streamer))