TANGO: addition of new symbol icon and minor fixes to others

Change-Id: I5e5c39fa8b237fd9a2e970e8f39ff6ff5a511c7d
Reviewed-on: https://gerrit.libreoffice.org/12206
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>