Resolve "Some data missing in substitutions table view"

Closes #76 (closed)

changed milestone to %2.0a2

added part::frontend prio::2 type::bug labels

added 5 commits

• 7771bb46 - Fix extra lesson query set
• f743746f - Use new subject template everywhere
• 7449f2ad - Show extra lessons in substitutions table
• 19c85222 - Show events in substitutions table
• 04baf821 - Fix groups display for events

Compare with previous version

@nik Please review.

unmarked as a Work In Progress

assigned to @nik

added 40m of time spent at 2020-04-21

mentioned in commit bea5efbe

merged