Add support setup default initializers for all deployment

This looks up a new configuration options called `brooklyn.deployment.initializers` (comma separated list). If specified on a Brooklyn instance, all deployments will load and execute these initializers. Theses classes are expected to be `EntityInitializer`, if an error occur (either cast or anything else) then the deployment will fail.

The code will try to:
1. load the class from the default class loader.
2. if (1) fails, it will try to load the class from the `TypeRegistry`. This is to allow execution of custom initializers that might be installed in the catalog later on.
3. if (1) and (2) fails, then the deployment is aborted.

karaf/features/src/main/resources/resources/etc/brooklyn.cfg

@@ -30,3 +30,7 @@ brooklyn.webconsole.security.provider = org.apache.brooklyn.rest.security.provid
 
 # Refer to the documentation for other auth settings, including LDAP, and other settings
 
+# Default initializers to automatically add to any application deployed with Brooklyn
+# This expect a comma separated list of initializer class names
+#brooklyn.deployment.initializers=
+