Use symbolic links for easier maintenance.

This makes it a lot easier to update the assets for the example... it's
automatic!
Allow user to specify a default image

When the `imageField` option is specified, we'll always show the
angucomplete-image-holder element. And if an image is found, we'll
render the angucomplete-image element, if not, we'll render the
angucomplete-image-default element.

The user can style the angucomplete-image-default element to provide a
default background image.
Add angucomplete-title class to title element

This allows us to style the title, specifically.
Merge pull request #5 from stevenharman/default-image-element

Default image element