Fix error on daily supervisions page

See merge request !289

Rename ugettext reference

See merge request !288

Resolve "Migrations fail with ProgrammingError"

Closes #195

See merge request !285

Merge branch '187-optimize-rendering-of-substituted-lessons-supervisions-on-daily-lessons-supervisions-page' into 'master'

Resolve "Optimize rendering of substituted lessons/supervisions on daily lessons/supervisions page"

Closes #187

See merge request !282

Resolve "AttributeError: 'NoneType' object has no attribute 'period'"

Closes #196

See merge request !286

Sort supervisions by period

Closes #190

See merge request !287

Resolve "Substitution form allows selecting students"

Closes #191

See merge request !283

Merge branch '186-fix-missing-pre-filtering-and-week-annotation-of-lessonperiods-on-daily-lessons-page' into 'master'

Resolve "Fix missing pre-filtering and week annotation of LessonPeriods on daily lessons page"

Closes #186

See merge request !281

Prepare release 2.5

See merge request !280

Resolve "Supervision Substitution entering"

Closes #185

See merge request !279

Resolve "[UI] Redesign Daily Lessons"

Closes #165

See merge request !276

Do release 2.4.2

See merge request !278

Merge branch '184-lessons-without-any-groups-are-displayed-as-cancelled-if-there-is-any-event-in-the-same-time' into 'master'

Resolve "Lessons without any groups are displayed as cancelled if there is any event in the same time period"

Closes #184

See merge request !277

Resolve "Selecting date in substitutions list yields NaN and 404"

Closes #183

See merge request !275

Fix equal lessons teachers

See merge request !274

Resolve "Use TimetableDataChangeTracker while managing substitutions"

Closes #181

See merge request !273

Drop support for GitHub

See merge request !272