[Framework] Bring in changes from sandbox

Bring in changes from 'sandbox' branch. These include:

* Reconfiguring require's baseUrl such that relative
  paths work as expected in define call dependencies.
  Previously this only worked as expected in the
  framework bundle, since data-main points there.
* Add support for a 'constants' category of extension,
  to define application constants from bundles. This
  allows services to treat static values (such as
  persistence URIs) as injectable dependencies.
* Various assurances that properties from extension
  definitions will be exposed upon resolved
  implementations, even after partial construction.

WTD-572.

platform/framework/src/register/ExtensionRegistrar.js

@@ -156,6 +156,9 @@ define(
             }
 
             function registerExtensionGroup(extensionGroup) {
+                // Announce we're entering a new phase
+                $log.info("Registering extensions...");
+
                 // Register all declared extensions by category
                 Object.keys(extensionGroup).forEach(function (category) {
                     registerExtensionsForCategory(