Rename EventPlanner to SemesterCalendar.
Remove useless TeachingTime <-> SemesterCalendar two-way dependency.
Introduce proper EventPlanner and move all event planning logic into it.
Remove unused Semester class.
Replace ScheduleManager planning specs with EventPlanning specs.
Parsing starts_at and ends_at strings in Event fabricator.
Add + operator to Period.
Refactor EventPlanner#renumber_events and add specs.
Change Event renumbering implementation to SQL.
Remove parallels loading in EventPlanner#plan_semester.
Add transactions to event planning.
Merge pull request #71 from cvut/event-planning-refactoring

Event planning refactoring.