update markup of controls: add second input field for better control
of values
update style of sliders; add styles for new input fields
remove html5slider polyfill

this polyfill is no longer needed since firefox 23 added support for
input sliders: https://bugzilla.mozilla.org/show_bug.cgi?id=344618#c56
(and i don't really care much for older firefox versions)

thanks @fryn for a great piece of code!
remove reference to html5slider
add support for number input fields and keep sliders and numbers in
sync
update control selector
Merge branch 'changes' into develop