Update fontinst docbook to 5.12
bump date + releaseinfo
remove kde-look.org/store.kde.org, there are no fonts available
add info about Unicode Blocks in kfontview preview
Differential Revision: https://phabricator.kde.org/D11831
(cherry picked from commit 31677cba0e71458106cf8909b1c8a00bb7b46a0d)
backport to 5.12 LTS