Left align on mobile form and buttons

Cherry picked from gh-1233.
Explanation from @cfarquharson:
"changes are to make sure that labels always left align in mobile and that the button-group classes are flush left in mobile (if you take any demo page and view it in mobile, the two buttons at the top below the H1 for the "Documentation" and "Questions and feedback" still retain their margin-left right but that should be remove in mobile so they are left aligned like everything else. "