Add type parameter to VariantMap::GetPtr funcition, so we can get correct type in Lua.
Remove SetCamera and GetCamera etc function in VariantMap, pls use SetPtr and GetPtr.

git-svn-id: http://urho3d.googlecode.com/svn/trunk@2604 3bd170d8-ddcf-f82c-f583-7a401ccf5608