Add option to delete sources with support in all three backends

webui/templates/sources/delete.tpl

@@ -0,0 +1,7 @@
+<h2>Delete Source</h2>
+
+<p>
+	Are you sure you want to delete {$source->plugin()|escape:"html"}:{$source->filename()|escape:"html"}?
+	[ <a href="{$base_uri}sources/delete/plugin/{$source->plugin()}/id/{$source->filenameEncoded()}/confirm" title="Delete it">Delete</a>
+	| <a href="{$base_uri}rips/sources" title="Return to sources list">Cancel</a> ]
+</p>