Customizable CSS, Logo url

New Features:

• Support for css color and font options in the config object
• Support for a logo url in the config object

Example configuation:

	layout: "footer",
	showFooterAfterSubmit: true,
	logoUrl: "https://www.example.com/image.png",
	css: {
		"color-primary": "#0a82be",
		"color-secondary": "#eaeaea",
		"color-border": "#eaeaea",
		"color-background": "#ffffff",
		"color-text-primary": "#333333",
		"color-text-secondary": "#0a82be",
		"color-linkColor": "#0a82be",
		"color-table-background": "#f7f7f7",
		"font-family": "'Noto Sans', 'Helvetica Neue', Helvetica, Arial, sans-serif",
		"custom-font-url": "https://fonts.googleapis.com/css?family=Noto+Sans",
	},

Things to note:

• When using the "footer" style instead of the modal intro screen; the image is forced to be a square shape.
• A custom font url must have the "font-family" css specified to take effect.
• A small change to the configuration file behavior: the publisher can specify as few keys as they would like with regards to the css and repromptOptions config fields. Before, they would have had to supply values for every key in the object.