Added a banner to the beta site

Just as a heads up for people who mentally or actually filter phpweb SVN commits: I've just made a commit that adds a banner to the top of the beta site explaining that it's a work in progress, could change at any moment, may cause imminent death, is probably broken, and that contents may settle during transit. The beta's getting some attention on Twitter and the like, so I felt it would be best to set the expectations up front that it's not the finished product, because some people are assuming that it is. The close button on the bar sets a cookie that prevents it from recurring for 30 days, so it shouldn't be too annoying for people actually trying to use it as their main site for testing purposes. (Or because they think it's pretty, like I do.) My apologies for the added ugliness and potential clunky wording. Commits to fix one or both welcome. :) Adam