Improve feature: Control the update from increments/variables table

[legija]

In large, complicated files, having the variables table update immediately after keystroke, makes it difficult (and very slow) to make changes to formulas under increments.

I propose to add an "apply", "cancel" and "ok" button to the variables table dialogue, after which all changes to the increments tab are then applied.

[Roman Telezhynskyi]

This change should be part of optimization improvements list.

[Roman Telezhynskyi]

Removing milestone: v0.6.0 (automated comment)