Provide search input placeholder="" support to IEs

[mdb]

Currently, the field on the homepage utilizes the HTML5 placeholder attribute to house its "Enter a Philadelphia address to find homeless shelters" text. I'm under the impression that this will not work across older versions of Internet Explorer.

Because -- as Robert mentioned -- many potential users will view the site in Internet Explorer, we'll need to provide some comparable placeholder-style functionality and directive for IE, presumably with a JavaScript workaround.