Add "grey" variants for "gray" colors

The non-American spelling of grey is widely supported, and explicitly
in the SVG color spec http://www.w3.org/TR/css3-color/#svg-color
Fixes gh-86
Fixes CSSLint/csslint#407

Author: nschonni

src/css/Colors.js

@@ -25,6 +25,7 @@ var Colors = {
     darkcyan        :"#008b8b",
     darkgoldenrod   :"#b8860b",
     darkgray        :"#a9a9a9",
+    darkgrey        :"#a9a9a9",
     darkgreen       :"#006400",
     darkkhaki       :"#bdb76b",
     darkmagenta     :"#8b008b",
@@ -36,11 +37,13 @@ var Colors = {
     darkseagreen    :"#8fbc8f",
     darkslateblue   :"#483d8b",
     darkslategray   :"#2f4f4f",
+    darkslategrey   :"#2f4f4f",
     darkturquoise   :"#00ced1",
     darkviolet      :"#9400d3",
     deeppink        :"#ff1493",
     deepskyblue     :"#00bfff",
     dimgray         :"#696969",
+    dimgrey         :"#696969",
     dodgerblue      :"#1e90ff",
     firebrick       :"#b22222",
     floralwhite     :"#fffaf0",
@@ -51,6 +54,7 @@ var Colors = {
     gold            :"#ffd700",
     goldenrod       :"#daa520",
     gray            :"#808080",
+    grey            :"#808080",
     green           :"#008000",
     greenyellow     :"#adff2f",
     honeydew        :"#f0fff0",
@@ -68,12 +72,14 @@ var Colors = {
     lightcyan       :"#e0ffff",
     lightgoldenrodyellow  :"#fafad2",
     lightgray       :"#d3d3d3",
+    lightgrey       :"#d3d3d3",
     lightgreen      :"#90ee90",
     lightpink       :"#ffb6c1",
     lightsalmon     :"#ffa07a",
     lightseagreen   :"#20b2aa",
     lightskyblue    :"#87cefa",
     lightslategray  :"#778899",
+    lightslategrey  :"#778899",
     lightsteelblue  :"#b0c4de",
     lightyellow     :"#ffffe0",
     lime            :"#00ff00",
@@ -126,6 +132,7 @@ var Colors = {
     skyblue         :"#87ceeb",
     slateblue       :"#6a5acd",
     slategray       :"#708090",
+    slategrey       :"#708090",
     snow            :"#fffafa",
     springgreen     :"#00ff7f",
     steelblue       :"#4682b4",
@@ -151,6 +158,7 @@ var Colors = {
     buttontext          :"Text on push buttons.",
     captiontext         :"Text in caption, size box, and scrollbar arrow box.",
     graytext            :"Grayed (disabled) text. This color is set to #000 if the current display driver does not support a solid gray color.",
+    greytext            :"Greyed (disabled) text. This color is set to #000 if the current display driver does not support a solid grey color.",
     highlight           :"Item(s) selected in a control.",
     highlighttext       :"Text of item(s) selected in a control.",
     inactiveborder      :"Inactive window border.",