Implements colour palette + UIColor conversion using Color palettes & resource dependencies on colour palettes.

* You can no define your colour palette in colours file.
  The first time a colour will be converted from a format that could be a colour from a palette, all the .colors files will get loaded.

* Here is a sample of a colors file :

{
    "MyApp" : {
        "lightBlue"   : "#50578f",
        "mediumBlue"  : "#192360",
        "blue"        : "#001841",
        "darkBlue"    : "#010f2a",
        "yellow"      : "#ffc21e",
        "orange"      : "#d5560f",
        "pink"        : "#cf3c60",
        "darkPink"    : "#911731",
        "lightPurple" : "#b49abf",
        "purple"      : "#8c4570",
        "lightGreen"  : "#bcc07e",
        "green"       : "#cadc23",
        "white"       : "#ffffff",
        "beige"       : "#eff2d3"
    }
}

* In a.style file, you can reference a colour from a palette as follow :

     "backgroundColor" : "MyApp.blue"

or

    "textColor" : "MyApp.orange"

* You can programatically request colours from the colour palettes as follow :

UIColor* color = [CKColorPalette colorWithKeyPath:@"MyApp.purple"];

or get the entire palette

NSDictionary* palette = [CKColorPalette colorPaletteWithKey:@"MyApp"];

colours files is part of the resource management behaviour which means, if colors files gets updated from dropbox, the colour palette AND the stylesheet that reference colours from the palette will get reloaded and the UI updated.