Updated to work with Sencha Touch 2.1+

-Added 'step' property to set helper increment value to the value
declared in instance config. Defaults to proxyConfig initial value.
Helper previously only incremented in whole numbers as  the proxyConfig
intial value is 1.
- Updated CSS to to fix slider ovlerlap bug. Slider now occupies
remaining 70% of div (helper occupies 30%; value unchanged).