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
Should listen at the document node rather than adding a listener to each element. Here is an example: https://github.com/wet-boew/wet-boew/blob/master/src/plugins/tabs/tabs.js#L767-L787

Also should use <code>.on( "click", selector + " summary", function() {</code> instead of <code>.click(</code>.