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.

Change-Id: I0750d49749ebaa28c7320cb374478fc6f9945fb7