Summarize double lessons

Double lessons are currently displayed (in HTML and PDF version) in two lines as

• Eb 3. HEG omission
• Eb 4. HEG omission

Shorter would be the following representation

• Eb 3. - 4. HEG omission

changed the description

assigned to @hansegucker

added part::frontend prio::2 source::customer type::feature labels

created merge request !105 (merged) to address this issue

mentioned in merge request !105 (merged)

closed with merge request !105 (merged)

mentioned in commit ad73a375