Overview: Refactor QML Plugins documentation and expand content

Refactor the QML Plugins, C++ Binding, and the Plugins tutorial:

The items in the new structure could be a separate page. There is existing content already, just refactoring and editing.
http://doc-snapshot.qt-project.org/5.0/qml-c-types.html
http://doc-snapshot.qt-project.org/5.0/qml-plugins.html
http://doc-snapshot.qt-project.org/5.0/qml-c-models-qdoc.html

Possible new structure:

A)C++ Types as QML Types
-Register a Type
-Exposing C++ Models
-Qt Objects and Interfaces
-Type Revisions and Versions
-Inheritance and Coercion
-Extension Objects
-Property Value Sources

B)C++ Properties and Methods
-Exposing Qt C++ Properties
-Default Property
-Grouped Properties
-Attached Properties
-Object and List Properties
-Sequence Types
-Property Signals
-Signals Support
-Exposing Methods

C)Registering a Plugin
Add a mini tutorial or summarize the steps

• QML Plugins (expand and edit the plugins page)

D)The "module API"