Fixed ISSUE-55662: Added missing blank_*.gif images

Tests: https://builds.openbravo.com/job/try-init/3836/console

blank images are images used in current backoffice Smartclient when there are no other specific image set.

If there is no image defiened, and the section component has blank.gif image defined, then blank_*_opened/closed.gif tries to be read, and without success because it does not exists.