Completely rewrite the slider

[sgomes]

mdl-slider is implemented with native styling on the HTML range element. This is causing a number of problems:

• Since these properties are all prefixed and behave slightly differently, we essentially have three different implementations.
• There are differences even within the same browser family (see Slider Thumb not showing in Microsoft Edge on Windows 10 #1625).
• There are hard to fix bugs due to the Material Design spec requiring things the native component doesn't expect (such as resizing the thumb, see Slider frustrating on mobile #1445).
• There are certain parts of the spec we simply can't implement in certain browsers, particularly around animations.
• The current implementation is incomplete, and only covers continuous sliders. Adding the rest would be very difficult, given the limitations above.

We should instead switch to a similar approach to the one we use in checkboxes and radio buttons, where we have a hidden native element for state and accessibility, and we render our own styling on top.