Add composite data display attributes support

This adds support for the new per-block display attributes
functionality in VTK. A new panel named "Multi-Block Inspector"
has been added which allows the user to toggle the visibility
of individual blocks in a multi-block dataset.

Change-Id: Iea7b458a04a2d4928f06d81bb9ed95389e263199
Merge topic 'composite-data-display-attributes' into next

db1633e Add composite data display attributes support