Allows user to define constant to disable scripts

Setting `LOAD_BS_SHORTCODES_SCRIPTS` to `false` (or anything other than `true`) will cause the function that loads the scripts to exit without enqueuing the scripts.

This is useful when users concatenate and uglify their JS.

NOTE: scripts load fine when constant is not defined.


This PR is one of many ways this could be accomplished. It was just the fastest way I could think of that will have a very minimal impact on your plugin.