STYLE: Make ordering of includes consistent

~~In general, the order is:~~

~~C standard library~~
~~C++ standard library~~
~~Boost~~
~~VXL~~
~~ITK~~
~~MetaIO~~
~~VTK~~
~~TubeTK~~

~~For .txx and .cxx files, the corresponding header is included first. For .h files the header of any superclass is included first. Within a grouping, headers are usually in alphabetical order.~~

Following the 3D Slicer header ordering rules for compatibility.

TubeTK
Boost
ITK
MetaIO
VCL/VNL
VTK
C standard library
C++ standard library

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