Medusa System Added

Read about the medusa system [here](https://nadekobot.readthedocs.io/en/latest/medusa/creating-a-medusa/)

src/Nadeko.Medusa/Strings/IMedusaStrings.cs

@@ -0,0 +1,15 @@
+using System.Globalization;
+
+namespace Nadeko.Snake;
+
+/// <summary>
+///     Defines methods to retrieve and reload medusa strings
+/// </summary>
+public interface IMedusaStrings
+{
+    // string GetText(string key, ulong? guildId = null, params object[] data);
+    string? GetText(string key, CultureInfo locale, params object[] data);
+    void Reload();
+    CommandStrings GetCommandStrings(string commandName, CultureInfo cultureInfo);
+    string? GetDescription(CultureInfo? locale);
+}