Changed VMs references to database singleton

Added some unit tests (WIP)

ModernKeePassApp.Test/Mock/DatabaseHelperMock.cs

@@ -0,0 +1,66 @@
+using System;
+using ModernKeePass.Interfaces;
+using ModernKeePass.ViewModels;
+using ModernKeePassLib;
+using ModernKeePassLib.Cryptography.KeyDerivation;
+using ModernKeePassLib.Keys;
+using Windows.Storage;
+
+namespace ModernKeePassApp.Test.Mock
+{
+    public class DatabaseHelperMock : IDatabase
+    {
+        public PwCompressionAlgorithm CompressionAlgorithm { get; set; }
+
+        public StorageFile DatabaseFile { get; set; }
+
+        public PwUuid DataCipher { get; set; }
+
+        public KdfParameters KeyDerivation { get; set; }
+
+        public string Name => "MockDatabase";
+
+        public GroupVm RecycleBin { get; set; }
+
+        public bool RecycleBinEnabled { get; set; }
+
+        public GroupVm RootGroup { get; set; }
+
+        public int Status { get; set; }
+
+        public void AddDeletedItem(PwUuid id)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Close()
+        {
+            throw new NotImplementedException();
+        }
+
+        public void CreateRecycleBin()
+        {
+            throw new NotImplementedException();
+        }
+
+        public void Open(CompositeKey key, bool createNew)
+        {
+            throw new NotImplementedException();
+        }
+
+        public bool Save()
+        {
+            throw new NotImplementedException();
+        }
+
+        public bool Save(StorageFile file)
+        {
+            throw new NotImplementedException();
+        }
+
+        public void UpdateCompositeKey(CompositeKey key)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}