Implemented opening/saving themes

Filtration.Common/Services/FileSystemService.cs

@@ -0,0 +1,36 @@
+using System;
+using System.IO;
+
+namespace Filtration.Common.Services
+{
+    public interface IFileSystemService
+    {
+        string ReadFileAsString(string filePath);
+        void WriteFileFromString(string filePath, string inputString);
+        bool DirectoryExists(string directoryPath);
+        string GetUserProfilePath();
+    }
+
+    internal class FileSystemService : IFileSystemService
+    {
+        public string ReadFileAsString(string filePath)
+        {
+            return File.ReadAllText(filePath);
+        }
+
+        public void WriteFileFromString(string filePath, string inputString)
+        {
+            File.WriteAllText(filePath, inputString);
+        }
+
+        public bool DirectoryExists(string directoryPath)
+        {
+            return Directory.Exists(directoryPath);
+        }
+
+        public string GetUserProfilePath()
+        {
+            return Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
+        }
+    }
+}