Render slider in form editor
Adds option to unset slider

Checkbox to left of slider allows for submission of empty value to the field. Also adds gsf_unset_slider filter to modify text of the checkbox label.
Removes size setting & version update

commit 0c5e67fb97e26d46457ee4a1a18a95d497b189eb
Author: UaMV <joshua.vandercar@gmail.com>
Date:   Wed Nov 12 13:46:51 2014 -0600

    Removes size setting & version update
Fix for unset/slider widths
Revert "Fix for unset/slider widths"

This reverts commit ea83cea5e289a8924a8875e5b43c561dc871b54d.
Revert "Adds option to unset slider"

This reverts commit a33527a5e232a9e66b4bf67b1b4ec0eb721a6b3b.
Readme edit