Internal refactoring of how plugin components are tagged/managed.

Made some class templates for code that seemed duplicated between
file/protocol tags and managers.  Seems like it helps a bit and
hopefully can be also be used to transition other things that have
enum value "tags" (e.g. logging writers, input readers) to the
plugin system.

src/DebugLogger.h

@@ -27,6 +27,7 @@ enum DebugStream {
 	DBG_INPUT,	// Input streams
 	DBG_THREADING,	// Threading system
 	DBG_FILE_ANALYSIS,	// File analysis
+	DBG_PLUGINS,
 
 	NUM_DBGS // Has to be last
 };