Fix #154 - Make knob size configurable

Fix #154 - Make knob size configurable

Description

I use paper-slider in metro-like tiles, and in order to make them look good, I give them a high --paper-slider-height.

Currently the knob size is fixed to 10px+ --paper-slider-height (and it's inside a knob container div of 30px + --paper-slider-height ). With big values of --paper-slider-height (let's say 10px), the knob looks too small.

I thought that a --paper-slider-knob-size would be a worthy and fitting addition to the CSS custom properties available for paper-slider.

Actual look

High --paper-slider-height without --paper-slider-knob-size:

Desired look

High --paper-slider-height with --paper-slider-knob-size, using the modified version on my fork:

Live Demo

Example: http://jsbin.com/pilogib/4/edit?html,output

Tested on

• [x ] Chrome
• Firefox
• Safari 9
• Safari 8
• Safari 7
• Edge
• IE 11
• IE 10