ENH: Restore Imaging/Core tests

Restore tests that were skipped during modularization

Change-Id: I9322f57f5919f863ae77659474b243b11152da39
Made the Filters modules a private dependency

This makes the vtkFilters* modules a private dependency of the
vtkRenderingCore library, and fixes any issues introduced in other
modules that implicitly relied on these modules.

Change-Id: I2421aa54fc5b9132e0b91ae404263c6f663822f2
Removed the final remnants of the Cg shader code

This is no longer supported, and should now be fully removed from VTK.

Change-Id: Ibb3c8f3ad7ad6308a0ebe2c4db19db16bf764a94
restore "missing rows" behavior to vtkHeatmapItem

Properly handle the case where the data table does not contain a row
for every leaf node in the tree.

This commit fixes a regression that probably occurred around commit
3ea804: when vtkTreeHeatmapItem was refactored into separate classes
for the dendrogram and the heatmap.

Change-Id: I07c5de340c7a7845cf2172c0cd7f334e3e46b932
Merge topic 'RestoreRenderingAnnotationTests' into master

b5e215e3 ENH: Restore Imaging/Core tests
Merge topic 'remove-cg' into master

3fba0968 Removed the final remnants of the Cg shader code
Merge topic 'rendering-filters-private' into master

3c67759b Made the Filters modules a private dependency
Merge topic 'support_missing_data' into master

e2711892 restore "missing rows" behavior to vtkHeatmapItem