Intensity Profile Function - closes #5

This MR replaces !480 (closed) due to change of source branch.

Add Profile button near the photometry tools in the toolbar Profile can be made along an arbitrary line or locked to horizontal / vertical by holding shift Profile shows a preview of the line to be cut Profile produces a GNUplot graph of pixel intensity against distance along the cut

• For mono images there is just one curve
• For RGB images there are 3 separate curves for R, G, B (also an option for a single luminance curve)
• There is an option to generate 3 equispaced parallel profiles with a configurable separation
• For CFA images there is a CFA mode which generates 4 profiles, one for each CFA channel
• Command interface is available
• Applicable to sequences (expect this would mostly be useful for batch processing of dedicated spectrograph images) Includes measurement using Ctrl-Shift-left button drag or from the profile dialogs

Closes #5 (closed)