Add image derivative programs and their circular versions for phase images

[ofgulban]

I decided to separate magnitude and phase image processing programs because the interface gets too clunky when the same program tries to handle both types of images.

Magnitude type image programs

• [x] LN2_GRADIENTS
• [x] LN2_LAPLACIAN
• [x] LN2_GRAMAG

Phase type image programs

• [x] LN2_PHASE_GRADIENTS
• [x] LN2_PHASE_LAPLACIAN
• [x] LN2_PHASE_JOLT (make this optionally output phase jump [phase gramag])

Other

• [ ] Polish the help menus
• [ ] Generate test data (e.g. radial toy models)