Remove infieldlabels

Removes the infield labels in favor of placeholders.

* [ ] needs to be tested in a bunch of browsers, currently only tested in latest Firefox & Chrome
* [x] add placeholder shim @PVince81 https://github.com/owncloud/core/issues/5568
* fixes the ability to paste via right-click and middle-click #1926 cc @msrex
* fixes an issue where it was difficult to paste into the password field on mobile cc @DeepDiver1975 
* fixes some autofill issues https://github.com/owncloud/core/issues/6486
* should fix #4945

Please review @owncloud/designers