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
Okay, but we still need Modernizr here, because the event is conflicting with the one in the details polyfill for browsers which require the polyfill. Am I understanding correctly that the goal is to not use Modernizr here?