Update external projects

[jcfr]

• Remove obsolete workaround including CTestUseLaunchers
• Remove unmaintained integration of KWStyle
• Remove unmaintained and unused OpenIGTLink external project
• Remove unmaintained and unused ZMQ external project
• Update ITK from v3.20.1 to v5.1.2
• Update DCMTK from DCMTK-3.6.1_20161102 to DCMTK-3.6.5

[jcfr]

I did not update VTK as the current external project aims to support both Qt4 and Qt5 and in Slice we removed Qt4 support a while back.

For reference, here is a prior discussion where we briefly discussed removing support for Qt 4.x, see https://github.com/commontk/CTK/pull/822#issuecomment-416983907

[jcfr]

Local build reported error with VTK:

Cloning into 'VTK'...
fatal: unable to connect to vtk.org:
vtk.org[0: 192.168.115.100]: errno=Connection refused

I will update it as well ...

[lassoan]

I did not update VTK as the current external project aims to support both Qt4 and Qt5 and in Slice we removed Qt4 support a while back.

Users can use whatever versions they need, but we can still set Qt 5 and VTK 8 or 9 as default when someone does not specify any VTK and Qt versions.

[jriesmeier]

FYI: DCMTK 3.6.6 has been released only recently.