Improves mobile dropkick + performance boost

• ADDITION : DK now reverts to the orginal selects on mobile while
still maintaining styled ".dk_toogle"
• ADDITION : Ability to force dropkick normal mobile through setting {
nativeMobile : false }
• IMPROVES : performance through chaining some operations
• IMPROVES : reset method
• FIX : setValue method now assesses the existence of the option in the
<select> before applying
• CLEAN : reload/refresh duplicated methods, now is just refresh
• CLEAN : things unused and redundant
Bring back themes filter gradient for IE < 8

Apply the gradient in the '.dk_toogle' instead of the '.dk_container' to
avoid IE to crash the plugin