Bug 29821: Add interface for generating barcodes using svc/barcode

Bug 29821: Add interface for generating barcodes using svc/barcode

This patch adds a new page providing an interface for generating
barcodes using svc/barcode. A form allows the user to choose various
parameters and see the resulting barcode image.

To test, apply the patch and rebuild the staff interface SCSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

- Go to the "Tools" home page. Follow the link to "Barcode image
  generator."
- On the barcode image generator page, confirm that there is a "Barcode
  image generator" link in the sidebar and that it is displayed with
  bold text.
- Test the features of the form:
  - Enter a numeric value in the "Barcode" field and tab out of the
    field or click "Show barcode" button. A barcode of type "Code39"
    should be shown with the text of the barcode included in the
    image below the barcode.
  - A text area below the barcode image should show the HTML used to
    generate the preview image.
    - Clicking in this textarea should automatically add the contents to
    the clipboard. You should be shown a message, "HTML copied to the
    clipboard."
  - Check the "hide text" checkbox. The barcode should be redisplayed
    without the text.
  - Check that changing the "barcode height" value is reflected
    correctly in the barcode image.
  - Try adding non-numeric data in the "Barcode" field. You should be
    shown an error message, "Barcodes of type [type]  must be numeric."
  - Test these other numeric barcode types: Code39, COOP2of5, EAN13,
    EAN8, IATA2of5, Industrial2of5, ITF, Matrix2of5, NW7, UPCA, and
    UPCE.

    Note that EAN13, EAN8, UPCA, and UPCE expect specific patterns. Test
    values (found here: https://barcode.tec-it.com/en/UPCE):

    EAN13: 978020137962
    EAN8: 9031101
    UPCA: 72527273070
    UPCE: 0123456

  - Change the barcode type to "QRcode."
    - The form should change, hiding the "Hide text" checkbox and
      showing a new ranger slider for "QR Code module size."
    - The barcode field should now be labeled "Text, URL, or barcode,
      etc"
    - The barcode field hint should change to a hint about QRcode
      dimensions.
    - Changing the "module size" slider should change the size of the
      generated QR code. As you change the slider the selected value
      should be reflected in the box.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>