Completely rewrite the slider

`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 #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 #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.