qt3scan - allow for raster_line_pause setting in position controller object

[gadamc]

A user may be need to control the raster_line_pause during a scan. Right now this is hard-coded into controllers
here:

qt3-utils/src/qt3utils/datagenerators/piezoscanner.py

Line 23 in 73bea2d

self.raster_line_pause = 0.150 # wait 150ms for the piezo stage to settle before a line scan

and here:

qt3-utils/src/qt3utils/applications/qt3scan/controller.py

Line 250 in 1a311c5

self.raster_line_pause = 0.150 # wait 150ms for the piezo stage to settle before a line scan

This value should probably be controlled by the position controller objects, such as,

qt3-utils/src/qt3utils/applications/controllers/nidaqpiezocontroller.py

Line 9 in 73bea2d

class QT3ScanNIDAQPositionController:

The application controller would obtain the raster_line_pause from the position controller.

This would then require the position controller interface to have a new property added, raster_line_pause somewhere here:

qt3-utils/src/qt3utils/applications/qt3scan/interface.py

Line 22 in 73bea2d