Allow users to specify a background color

[evanugarte]

as part of the profile page, lets add a simple input that once edited and saved, the users background icon in the top right corner changes color.

game plan

• follow dessert problem
• add a new field to the user.js model called backgroundColor
• add allow the user edit api to update the backgroundColor, if specified
• in the frontend, render the updated user background color, after the color is updated
• add logic in the profile icon to default to the current gray color if the users profile color is not specified
• add logic in the profile icon to determine if the text should be rendered white or black https://stackoverflow.com/a/3943023