pairwise viz: add chart editor for downloads

[pverkind]

open as modal

• include URL (default: true, at the bottom)
• include metadata labels (author + title + ID for both books)
• adjust font size
• edit chart dimensions
• color customization
• highlight milestone( range)s

[pverkind]

first steps in commit #9a38112 :

• include URL option
• adjust font size (does not yet work for one-to-many viz)
• edit chart dimensions: fields are there but do not effect the output yet

[pverkind]

Current status:

• include URL (default: false)
• include metadata labels (author + title + ID for both books)
• adjust tick font size
• label font size
• edit chart width in mm and resolution in dpi
• edit chart height
• color customization
• highlight milestone( range)s