[WIP] 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
* 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 

Please review @owncloud/designers