Add hash files for test data and baselines

Change-Id: I6f73d5cb4d099c3ca8c78ca580c3a46500a313c8
cmake: Copy ExternalData files from VTK

They aren't present in older CMake versions and must be provided
manually.

Change-Id: I57f6301e4e881be49c27bb110957fad290a6442b
Add scripts to work with ExternalData

These scripts deal with baselines for new tests.

Change-Id: I404b4255f181faa81994eca2786635e9357ceece
Add support for Gerrit with ExternalData

Change-Id: I6a7a9b5a147c992d5a61e163331342892ea73e7b
Set up variables for ExternalData usage

Change-Id: I5a972b249e6be3922a03d3866e28ca9d96574eb6
Add functions wrapping VTK's test functions

These override the proper variables so that ParaView tests see the
correct directories and binaries.

Change-Id: I76ce7945b24e6898939de54e573908e45d555bff
Update pvpython tests to use ExternalData

Change-Id: Id3ba1cc6cbfe5e565f719d4631f9a38c00a25714
Update CoProcessing tests to use ExternalData

Change-Id: I14df8fcb7a58caa5aeed070d3c403506a351d58f
Update PythonCatalyst tests to use ExternalData

Change-Id: I85c9a3894c7febb45195cdcfa9ad657ddcb75ff2
Update ClientServerCore tests to use ExternalData

Change-Id: I639ca86ca3776bb6c11a0e5b02ddd4f461bf07cb
Update ClientServerStream tests to use ExternalData

Change-Id: I91d6d89562fa66d43562b9c00f8415c45d5ee0df
Update PVCommon tests to use ExternalData

Change-Id: I5d9270411b3ddc7b858fcf7780bca870e27840e5
Update ServerImplementation tests to use ExternalData

Change-Id: I2d85f9f5f82fad6b3f76d25e99a97823348d5884
Update ServerManager C++ tests to use ExternalData

Change-Id: I2dbee689363af8dce771a45cdd97cd72f4bfb793
Update ServerManager Python tests to use ExternalData

Change-Id: I2c0567cafce920272a8b0c5e19f963414009c307
Update PVRendering tests to use ExternalData

Change-Id: I729a4ed83f715b70fb26900789de17e840c79b92
Update ServerManagerWeb tests to use ExternalData

Change-Id: I17b590c68687a787399820ba3c6f52d612a78fd8
Update VTKExtensions tests to use ExternalData

Change-Id: I12a35a26a6dedc4a64c3d9b6dc14b6faa1c3a573
Update SciberQuestToolKit tests to use ExternalData

Change-Id: Ia4dac5d8503a116aadbdca248927932636ee0513
Update MantaView tests to use ExternalData

Change-Id: I46e1d0b8ff9deca6229166c07fe9a469a1aa404b