fdo#56116 : Names of bookmarks should allow all characters which
 are valid in HTML anchor names (missing: ':' and '.')

Change-Id: I44f1d1135067103fdcc7482793371c5b95c14cec
Reviewed-on: https://gerrit.libreoffice.org/12466
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>