osx improvements - rgba, opacity, and bug fixes

Changes made:

* Bundled with new osx_picker that:
* Correctly takes in any color format 
* Shows and manipulates opacity
* Outputs smartly to hex or rgba depending on opacity - (see https://github.com/lifedispenser/color-pick/tree/rgba)

* Replaces correctly hex and color names
* Replaces (almost) correctly rgb(a) values
Note: If there are two or more rgb(a) values in one line, it will only replace the first. 

Wish List:
* Figure out regex that will only replace the rgba that your cursor is on
* Figure out how to have custom NSColorpanels be the default mode in color_picker (like http://www.antetype.com/blog/2014/03/updated-antetype-color-picker-1-4-1/)

I haven't tested the changes on Linux or windows, so I am hesitant to recommend a push without further testing. However, if any mac users are fed up with a buggy color picker in sublime, feel free to use these changes by installing the package manually, here: https://github.com/lifedispenser/ColorPicker-1