add mysql database provider (#1375)

* refactor sqlite into separate library

* support mysql

* fixes

* sql fixes

* cleanup

* update changelog

ErsatzTV.Infrastructure.Sqlite/Migrations/20210225153055_RemoveOldMediaSources.cs

@@ -0,0 +1,15 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace ErsatzTV.Infrastructure.Sqlite.Migrations
+{
+    public partial class RemoveOldMediaSources : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder) =>
+            // remove old source/folders
+            migrationBuilder.Sql(@"DELETE FROM MediaSources WHERE Id NOT IN (SELECT MediaSourceId FROM Library)");
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+        }
+    }
+}