Make dials.predict step explicit

[dagewa]

Related to #8 and other issues.

Running dials.predict automatically after every step is expensive, and for some steps it is irrelevant. An improvement would be to only run dials.predict when a "predict" button is pressed This button could be located near to Reflection Type:

In addition, this list should contain one extra type:

• Integrated

and if integrated.pickle exists, this ought to be used to display the overlays (like dials.image_viewer behaviour)