Adds abstract File, Script, Stylesheet and Template model implementations for U4-933 U4-934 U4-935

Added a CssParser which is used internally by the Stylesheet class, but still needs a bit of work - primarily testing.
Resolves a couple of naming conflicts for Template.

src/Umbraco.Core/Models/Script.cs

@@ -0,0 +1,52 @@
+using System.Linq;
+using Umbraco.Core.Configuration;
+using Umbraco.Core.IO;
+
+namespace Umbraco.Core.Models
+{
+    /// <summary>
+    /// Represents a Script file
+    /// </summary>
+    public class Script : File
+    {
+        public Script(string path) : base(path)
+        {
+            base.Path = path;
+        }
+
+        /// <summary>
+        /// Boolean indicating whether the file could be validated
+        /// </summary>
+        /// <remarks>
+        /// The validation logic was previsouly placed in the codebehind of editScript.aspx,
+        /// but has been moved to the script file so the validation is central.
+        /// </remarks>
+        /// <returns>True if file is valid, otherwise false</returns>
+        public override bool IsValid()
+        {
+            //NOTE Since a script file can be both JS, Razor Views, Razor Macros and Xslt
+            //it might be an idea to create validations for all 3 and divide the validation 
+            //into 4 private methods.
+            //See codeEditorSave.asmx.cs for reference.
+
+            var exts = UmbracoSettings.ScriptFileTypes.Split(',').ToList();
+            if (UmbracoSettings.EnableMvcSupport)
+            {
+                exts.Add("cshtml");
+                exts.Add("vbhtml");
+            }
+
+            var dirs = SystemDirectories.Scripts;
+            if (UmbracoSettings.EnableMvcSupport)
+                dirs += "," + SystemDirectories.MvcViews;
+
+            //Validate file
+            var validFile = IOHelper.ValidateEditPath(Path, dirs.Split(','));
+
+            //Validate extension
+            var validExtension = IOHelper.ValidateFileExtension(Path, exts);
+
+            return validFile && validExtension;
+        }
+    }
+}