Flickr: Added support for cc-zero & public domain mark

• cc-zero images are handled like other images with the license tag of "{{FlickrVerifiedByUploadWizard|cc-zero}}{{cc-zero}}"
• public domain mark images are handled with:
  • set "{{FlickrVerifiedByUploadWizard|Public Domain Mark}}" as the prefix for the license tag
  • set the license boolean parameter to false to indicate that the exact license tag is uncertain
    • The boolean value was originally added in Ice8d3a
    • the value was always true, and false seemed to be meaningless
  • when the value is false, a textbox input is added for the custom pd license tag
    • The default configuration does not allow the textbox to be blank
  • Final output is something like (before substitution):

**: "{{FlickrVerifiedByUploadWizard|Public Domain Mark}}{{subst:Custom license marker added by UW}}\n{{PD-blah}}"

Bug: T105629
Change-Id: If6e402