Cleaned up the Console bot. Added PluginNotFoundException

DiscordBotCore/Others/Exceptions/PluginNotFoundException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace DiscordBotCore.Others.Exceptions
+{
+    internal class PluginNotFoundException : Exception
+    {
+        public PluginNotFoundException(string pluginName) : base($"Plugin {pluginName} was not found") { }
+
+        public PluginNotFoundException(string pluginName, string url, string branch) :
+            base ($"Plugin {pluginName} was not found on {url} (branch: {branch}") { }
+    }
+}