Menu item keyboard accelerators implemented (#589)

* Added icon to "Recent >" menu item.

* Refactored app menu implementation, and implemented keyboard accelerators. Still doesn't work though.

* Few things fixed, but still doesn't work.

* Clicking menu items works.

* Fixing an issue with resources.

* New menu binding implemented. Still doesn't work though.

* Menu displayed properly, except for "Settings".

* Menu works, but it doesn't refresh.

* Works. But needs to be polished.

* All known issues with the new app menu solved.

* Significantly simplifying app menu binding.

* Removing some obsolete classes.

* Menu binding mechanism additionally optimized for performances.

* Removing unused translations.

* Further refactoring app menu binding, in order to make it more general.

* New window mechanism simplified. Terminal-launching code refactored to be more readable. A bug with "SSH Info" fixed.

* Merging the latest changed.

FluentTerminal.App.ViewModels/Menu/MenuItemKeyBindingViewModel.cs

@@ -0,0 +1,147 @@
+using FluentTerminal.Models;
+using GalaSoft.MvvmLight;
+
+namespace FluentTerminal.App.ViewModels.Menu
+{
+    public class MenuItemKeyBindingViewModel : ViewModelBase
+    {
+        #region Properties
+
+        private int _key;
+
+        public int Key
+        {
+            get => _key;
+            set => Set(ref _key, value);
+        }
+
+        private int _keyModifiers;
+
+        // Corresponds to https://docs.microsoft.com/en-us/uwp/api/windows.system.virtualkeymodifiers
+        public int KeyModifiers
+        {
+            get => _keyModifiers;
+            private set => Set(ref _keyModifiers, value);
+        }
+
+        private bool _ctrl;
+
+        public bool Ctrl
+        {
+            get => _ctrl;
+            set
+            {
+                if (Set(ref _ctrl, value))
+                {
+                    SetKeyModifiers();
+                }
+            }
+        }
+
+        private bool _alt;
+
+        public bool Alt
+        {
+            get => _alt;
+            set
+            {
+                if (Set(ref _alt, value))
+                {
+                    SetKeyModifiers();
+                }
+            }
+        }
+
+        private bool _shift;
+
+        public bool Shift
+        {
+            get => _shift;
+            set
+            {
+                if (Set(ref _shift, value))
+                {
+                    SetKeyModifiers();
+                }
+            }
+        }
+
+        private bool _windows;
+
+        public bool Windows
+        {
+            get => _windows;
+            set
+            {
+                if (Set(ref _windows, value))
+                {
+                    SetKeyModifiers();
+                }
+            }
+        }
+
+        #endregion Properties
+
+        #region Constructors
+
+        public MenuItemKeyBindingViewModel(int key = 0, bool ctrl = false, bool alt = false, bool shift = false,
+            bool windows = false)
+        {
+            _key = key;
+            _ctrl = ctrl;
+            _alt = alt;
+            _shift = shift;
+            _windows = windows;
+
+            SetKeyModifiers();
+        }
+
+        public MenuItemKeyBindingViewModel(KeyBinding keyBinding) : this(keyBinding.Key, keyBinding.Ctrl,
+            keyBinding.Alt, keyBinding.Shift, keyBinding.Meta)
+        {
+        }
+
+        #endregion Constructors
+
+        #region Methods
+
+        private void SetKeyModifiers()
+        {
+            // Based on VirtualKeyModifiers enum values (https://docs.microsoft.com/en-us/uwp/api/windows.system.virtualkeymodifiers)
+            var result = 0;
+
+            if (_ctrl)
+            {
+                result |= 1;
+            }
+
+            if (_alt)
+            {
+                result |= 2;
+            }
+
+            if (_shift)
+            {
+                result |= 4;
+            }
+
+            if (_windows)
+            {
+                result |= 8;
+            }
+
+            KeyModifiers = result;
+        }
+
+        public bool EquivalentTo(MenuItemKeyBindingViewModel other)
+        {
+            if (ReferenceEquals(this, other)) return true;
+
+            if (other == null) return false;
+
+            return _key == other._key && _keyModifiers == other._keyModifiers;
+        }
+
+        #endregion Methods
+    }
+}