Add 'Show All Blocks' button to context-menu

This adds a new button to the context-menu for multi-block
data sets which sets the visibility of all blocks to true.

Change-Id: I17044090cd128c627ec497906f2a78a62da9f7bd
Merge topic 'show-all-blocks' into next

ddb0cdf Add 'Show All Blocks' button to context-menu