IterationProxy for controlled access to embedded containers.
Switch access to SystemBody::m_children to IterationProxy interface.
Switch access to Space::m_bodies to IterationProxy interface.
Switch access to Frame::m_children to IterationProxy interface.
Switch access to UI::Container::m_widgets to IterationProxy interface.
Switch access to Lang::Resource::m_strings to IterationProxy interface.
Updated COMPILING.txt to remove 2008, 2010 and 2012 references to Visual Studio products.
Also update the changelog
Merge pull request #2784 from fluffyfreak/update-compiling

Merging
Merge branch 'iteration_proxy'