D14654: Add API for signature form field, and other helper classes

[Albert Astals Cid]

aacid commandeered this revision.
aacid edited reviewers, added: chinmoyr; removed: aacid.

REPOSITORY
  R223 Okular

REVISION DETAIL
  https://phabricator.kde.org/D14654

To: aacid, chinmoyr
Cc: okular-devel, ngraham, darcyshen, aacid