Added hex support

We use hex values to create UIColor and I like these functions: 
```
+ (NSColor *)colorWithRGBHex:(UInt32)hex alpha:(CGFloat)alpha;
+ (NSColor *)colorWithRGBHex:(UInt32)hex;
```

Their source can be easily found: https://github.com/eploko/EPLAppKit/blob/master/EPLAppKit/NSColor%2BEPLAppKit.m

Also I like this hex color picker plugin: http://wafflesoftware.net/hexpicker/
There are changes to work with the functions and the plugin using ColorSense-for-Xcode.