Added dismissible alert plugin

This is the cleaned up version of https://github.com/wet-boew/wet-boew/pull/5932.
Please note the build will fail because of this issue: https://github.com/wet-boew/wet-boew/issues/5927
All it takes is a single setTimeout and it all breaks (which the Modernizr code does include a setTimeout in the Yepnope portion). Because even through JavaScript is synchronous, it doesn't mean that it executes from top to bottom with no interruptions (just means you don't have two threads running in parallel). So you should be sure to make your code safe from race conditions since we've had no end of headaches from race conditions in the past (with and without events). They are one of the most difficult things to diagnose so it is best to safeguard where we can.