Brushes - Added brush presets

ColorGradient - Refactored so it implements IList

src/Artemis.UI/Screens/ProfileEditor/Dialogs/LayerBrushPresetView.xaml

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+<UserControl x:Class="Artemis.UI.Screens.ProfileEditor.Dialogs.LayerBrushPresetView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:s="https://github.com/canton7/Stylet"
+             xmlns:layerBrushes="clr-namespace:Artemis.Core.LayerBrushes;assembly=Artemis.Core"
+             xmlns:shared="clr-namespace:Artemis.UI.Shared;assembly=Artemis.UI.Shared"
+             mc:Ignorable="d"
+             d:DesignHeight="450" d:DesignWidth="800">
+    <StackPanel Margin="16">
+        <TextBlock Style="{StaticResource MaterialDesignHeadline6TextBlock}">
+            Select a brush preset
+        </TextBlock>
+
+        <ListBox ItemsSource="{Binding Presets}" SelectedItem="{Binding SelectedPreset}" HorizontalContentAlignment="Stretch" Margin="0 8 0 16">
+            <ListBox.ItemTemplate>
+                <DataTemplate DataType="{x:Type layerBrushes:ILayerBrushPreset}">
+                    <Border x:Name="Border" Padding="8" BorderThickness="0 0 0 1" BorderBrush="{DynamicResource MaterialDesignDivider}">
+                        <Grid>
+                            <Grid.ColumnDefinitions>
+                                <ColumnDefinition Width="Auto"/>
+                                <ColumnDefinition />
+                            </Grid.ColumnDefinitions>
+                            <shared:ArtemisIcon Icon="{Binding Icon}" VerticalAlignment="Center" Width="30" Height="30"/>
+                            <StackPanel Margin="8 0 0 0" Grid.Column="1">
+                                <TextBlock FontWeight="Bold" Text="{Binding Name}" />
+                                <TextBlock Text="{Binding Description}" />
+                            </StackPanel>
+                        </Grid>
+                    </Border>
+                </DataTemplate>
+            </ListBox.ItemTemplate>
+        </ListBox>
+
+        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
+            <Button Style="{StaticResource MaterialDesignFlatButton}" IsDefault="True" Margin="0 8 8 0" Command="{s:Action Cancel}">
+                USE DEFAULT SETTINGS
+            </Button>
+        </StackPanel>
+    </StackPanel>
+</UserControl>

src/Artemis.UI/Screens/ProfileEditor/Dialogs/LayerBrushPresetViewModel.cs

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+using System.Threading.Tasks;
+using Artemis.Core.LayerBrushes;
+using Artemis.UI.Shared.Services;
+using Stylet;
+
+namespace Artemis.UI.Screens.ProfileEditor.Dialogs
+{
+    public class LayerBrushPresetViewModel : DialogViewModelBase
+    {
+        private ILayerBrushPreset _selectedPreset;
+
+        public LayerBrushPresetViewModel(BaseLayerBrush layerBrush)
+        {
+            Presets = new BindableCollection<ILayerBrushPreset>();
+            Presets.AddRange(layerBrush.Presets);
+        }
+
+        public BindableCollection<ILayerBrushPreset> Presets { get; }
+
+        public ILayerBrushPreset SelectedPreset
+        {
+            get => _selectedPreset;
+            set
+            {
+                SetAndNotify(ref _selectedPreset, value);
+                SelectPreset(value);
+            }
+        }
+
+        public void SelectPreset(ILayerBrushPreset preset)
+        {
+            preset.Apply();
+            Execute.OnUIThreadAsync(async () =>
+            {
+                await Task.Delay(250);
+                Session?.Close(true);
+            });
+        }
+    }
+}