Expose 'getter' for MOAIViewport to lua

Expose 'getter' for MOAIViewport to lua for introspection purposes:
 - getSize()
 - getScale()
 - getOffset()
Merge branch 'feature-MOAIViewport_accessors' into nanocell-development
Add support for external "moai-components".

Add support for external "moai-components" to allow MOAI to non-intrusively
add proprietary game engine components without having to directly
modify the MOAI code base.

The main motivation for this feature is have a clear separation between
the public MOAI code base and proprietary components. This enables
developers to easily implement/exposed patches and features to the public
code without having to release proprietary game code.
Merge branch 'feature-moai_components' into nanocell-development