Move exec and events components to util module

The exec and events components are common components that
are used by both runtime and registry. It makes sense to
move them into the util package.

This also adds some docs to the registry module

packages/node_modules/@node-red/registry/lib/localfilesystem.js

@@ -16,9 +16,6 @@
 
 var fs = require("fs");
 var path = require("path");
-
-var log;
-
 var log = require("@node-red/util").log;
 var i18n = require("@node-red/util").i18n;
 
@@ -26,8 +23,8 @@ var settings;
 var disableNodePathScan = false;
 var iconFileExtensions = [".png", ".gif", ".svg"];
 
-function init(runtime) {
-    settings = runtime.settings;
+function init(_settings) {
+    settings = _settings;
 }
 
 function isIncluded(name) {