Major OpenDatabaseUserControl refactor, now has proper ViewModel

Status text and password box border colors are updated according to database status
Update composite key in Settings work
Some code cleanup

ModernKeePass/Converters/DoubleToSolidColorBrushConverter.cs

@@ -0,0 +1,31 @@
+using System;
+using Windows.UI;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml.Media;
+
+namespace ModernKeePass.Converters
+{
+    public class DoubleToSolidColorBrushConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            try
+            {
+                var currentValue = (double) value;
+                var maxValue = double.Parse(parameter as string);
+                var green = System.Convert.ToByte(currentValue / maxValue * byte.MaxValue);
+                var red = (byte) (byte.MaxValue - green);
+                return new SolidColorBrush(Color.FromArgb(255, red, green, 0));
+            }
+            catch (OverflowException)
+            {
+                return new SolidColorBrush(Color.FromArgb(255, 0, byte.MaxValue, 0));
+            }
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}