Fix login fields

* fix log in input sizing caused by core input field switch to px https://github.com/owncloud/core/pull/7916 (also some code style fixes) cc @PVince81 @MorrisJobke 
* make infield labels use less space so pasting in is easier cc @msrex (you can right- or middle-click anywhere in the field which is _not_ on the text to paste)

Please review @owncloud/designers