Twenty Eleven: theme options - see #17198

 * First pass at Link Color CSS rules
 * Add new function to return default values
 * Implement better validation for hex color value
 * Fix missing esc_attr()

git-svn-id: https://core.svn.wordpress.org/trunk@17732 1a063a9b-81f0-0310-95a4-ce76da25c4cd