Implements Hide / Display for the Password Toggle Button

A fix for https://github.com/owncloud/core/issues/2435
Thanks to @houqp for the help. :+1: 
It works fine in the Personal Settings, but there might be a problem with Chrome Autofills on the Installation and Login page. I tried fixing it by using <code>setTimeout();</code> and checking the input every 200ms for anything being there, but it isn't working in all test cases. 
Can anyone with a more knowledge about autofills help here? @Raydiation @houqp @jancborchardt ? 
In all other cases, it works just fine.