Plugins hotspots support
This MR introduce the required code to support plugins extention through hotspots. This is a generic way that must be used to add specific plugins hotspots, as can been seen in FooPlugin.
Also, it is not necessary to declare the hotspot in Noosfero::Plugin class. All you need is implement the method plugin_hotspots returning an array with your plugin's hotspot name and document their use in the main plugin class.
This MR also introduce a new hotspot in LDAP plugin to manipulate the person data before user creation.
This MR substitutes the old MR !507 (closed)