LPS-44185 This is related with previous pull (please read comment)

Hey @johnnyhowey, 

This is a basic implementation in notifications portlet for the mechanism of open dialog I've implemtented in https://github.com/johnnyhowey/liferay-portal/pull/43

This pull is just a proposal. I send this to you so you can see the whole picture. Anyway, it's fully functional for portal logic, but Plugins Repo UserNotification Handlers changes have not been implemented yet.

 If you like this solution, as soon as you push it, I'll update them.