updated event migration

added autoincrement id and filename
which is used for deleting events

db/migrations/1624829187_create_events.h

@@ -8,11 +8,13 @@ namespace db {
       public:
       m1624829187_create_events() : Migration() {
         db_builder::Table create_events = db_builder::Table::create("events"
-                                                          ).text("uid", "NOT NULL"
+                                                          ).integer("id", "NOT NULL PRIMARY KEY"
+                                                          ).text("uid", "NOT NULL UNIQUE"
                                                           ).text("summary", "NOT NULL"
                                                           ).integer("dtstart", "NOT NULL"
                                                           ).integer("dtend", "NOT NULL"
                                                           ).text("location"
+                                                          ).text("filename", "NOT NULL"
                                                           ).close();
         m_statement = create_events.str();
       }