Add CLI for automation

[spillerrec]

Add a CLI to make it possible to automate stitching to some degree. Following options should be usable:
Preprocess

• Alpha mask
• De-telecine
• Crop

Merging

• Vertical and Horizontal
• Precision
• All methods, except animation and layers (not ready)

Render and color

• All options

Postprocess

• Scaling
• Deconvolve
• Level
• Binarize

To do this we need to separate the stitching pipeline from the GUI, as it is currently embedded in mainwindow.cpp. At the same time, add the possibility to have separate frames for animation, and reusable alpha masks. Also think about how to specify separate small animations in different parts of the image.

Furthermore, since this is primarily a GUI application, if it is loaded with just images, it should add them in the GUI automatically. Also allow dropping an entire folder, to load all the images therein.

[spillerrec]

Now prevents the gui from starting with option --no-gui, and supports basic loading, aligning, rendering, and saving.

[spillerrec]

Difference::SimpleSettings does not parse properly due to being a multi valued structure. We need some way of handling those