Fix code style issues.
Add item creation with suffixes.

- More than one item can be added at once by giving a list of suffixes.
Restyle the price tag form.

- Use bootstrap styles because it's easy, although a bit verbose.
- Add option for tiny price tags.
- Add help text.
Show price tags from newest to oldest.
Add tiny price tags.
Implement 1px high PNGs and make PNGs default format.

- Added a custom writer based on the ImageWriter that renders the barcode
  as 1px high PNG. Size from 2000 bytes to 120 bytes.
- Also removes text from images and positions the html text below the barcode.