FormLayout: Accept HTML form attributes as config options

Working towards making the FormLayout actually usable as a form.

Added a proper PHP FormLayout example. It looks kinda busted visually
(no margin between it and next/previous ones, seemingly random spacing
inside), but I'll leave this for somebody else to figure out.

Change-Id: I96c13cb52fe583e70a19ed6e530704933419f742
Merge "FormLayout: Accept HTML form attributes as config options"