Tweak layout of register form @ various sizes from Sam's input

The main change is that the captcha snaps to the width of the left
column, or the full width when xs is active.

The alignment of the T&C checkbox & text was changed.

The layout now stays the same (2 column, label & input on same line)
until xs is active (previously changed between md and lg). xs uses 1 col
with labels and inputs on separate lines as before.
Remove "below" from captcha error as the message is below the input
Alphabetise the order of some registration CSS properties