add slider minify scripts option

define DS_MIN_SCRIPTS as true to minify slider-pack script, false to not minify it, and if it's not defined then the script is minified by default.
let child themes override enqueue scripts function

wrap enqueuing function with function_exists so child can override it.
Rename jquery.slider-pack.js to jquery.slider-pack.1.1.js

rename to allow DS_MIN_SCRIPTS to work.
Merge pull request #41 from ryanjkoehler/min_scripts

add minify slider script option