Return school-term for statistics-by-person-query

Query can send no school-term and will receive the result for the
current school-term. With the additional school-term parameter the
frontend now knows which school-term is current.

aleksis/apps/alsijil/frontend/components/coursebook/statistics/statistics.graphql

 fragment statistics on StatisticsByPersonType {
+  schoolTerm
   participationCount
   absenceCount
   absenceReasons {

aleksis/apps/alsijil/schema/statistics.py

@@ -27,6 +27,7 @@ class ExtraMarkWithCountType(graphene.ObjectType):
 
 
 class StatisticsByPersonType(graphene.ObjectType):
+    school_term = graphene.Int()
     participation_count = graphene.Int()
     absence_count = graphene.Int()
     absence_reasons = graphene.List(AbsenceReasonWithCountType)
@@ -34,6 +35,9 @@ class StatisticsByPersonType(graphene.ObjectType):
     tardiness_count = graphene.Int()
     extra_marks = graphene.List(ExtraMarkWithCountType)
 
+    def resolve_school_term(root, info):
+        return 1
+
     def resolve_participation_count(root, info):
         return 3