Added Hue Only and Color Only options (`showHue: bool`, `showColor bool`)

Added `showHue` and `showColor` options to show/hide the main color box and hue box.

For example in the Hue-only mode(`showColor: false`, set the `color` property to the appropriate saturation/lightness and then the user can select a Hue.

If you want the user to choose a shade (saturation, lightness). Then use the color-only mode(`showHue: false`) and first set the appropriate hue using the `color` property.

```
// Make the normal color input
$('.colorpicker.normal').spectrum({
	color: "#f00"
	//allowEmpty: true
	//showAlpha: true
});

// Hue only input
$('.colorpicker.hue-only').spectrum({
	color: "#f00",
	//allowEmpty: true,
	//showAlpha: true,
	clickoutFiresChange: true, // Not necessary because of `showButtons: false` but nice to have
	showButtons: false,
	showColor: false
});

// Color only input
$('.colorpicker.color-only').spectrum({
	color: "#f00",
	//allowEmpty: true,
	//showAlpha: true,
	showHue: false
});
```

Works with any existing options: ex. `showButtons` and `showAlpha`