Add basic activity log (#141)

* Add basic activity log

* Add database migration

* Fix layout

* Fix types

---------

Co-authored-by: Sebastien Castiel <sebastien@castiel.me>

prisma/schema.prisma

@@ -17,6 +17,7 @@ model Group {
   currency     String        @default("$")
   participants Participant[]
   expenses     Expense[]
+  activities   Activity[]
   createdAt    DateTime      @default(now())
 }
 
@@ -80,3 +81,21 @@ model ExpensePaidFor {
 
   @@id([expenseId, participantId])
 }
+
+model Activity {
+  id            String       @id
+  group         Group        @relation(fields: [groupId], references: [id])
+  groupId       String
+  time          DateTime     @default(now())
+  activityType  ActivityType
+  participantId String?
+  expenseId     String?
+  data          String?
+}
+
+enum ActivityType {
+  UPDATE_GROUP
+  CREATE_EXPENSE
+  UPDATE_EXPENSE
+  DELETE_EXPENSE
+}