feat: initial datamodel + ef connection and migrations

Initial version of the data model
Includes EF initialization and migrations
EF migrations are applied on application start

TournamentOrganizer/Views/MainWindow.axaml

@@ -0,0 +1,12 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:TournamentOrganizer.ViewModels"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:views="using:TournamentOrganizer.Views"
+        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        x:Class="TournamentOrganizer.Views.MainWindow"
+        Icon="/Assets/avalonia-logo.ico"
+        Title="TournamentOrganizer">
+        <views:MainView />
+</Window>