Change plot dialogs to be non-modal
Change plot dialogs to be non-modal

This changes the plot dialogs to be non-modal so multiple
data dialogs can be used simultaneously.

Change-Id: Ib9ba623737e562f87e3f27b33a8e5fceccadcd28

OpenChemistry/mongochem,OpenChemistry/mongochem,OpenChemistry/mongochem