style(transport_helper): rename db_insert functions

On classes with relational tables, the insert function for the table
that matches the actual class (not relation), is now just called dbInsert
instead of dbInsertClassname.
For inserting to relational Tables, the name stays more descriptive
about the relation covered

lib/transport_helper.dart

@@ -111,7 +111,7 @@ class Route {
     """);
   }
 
-  void dbInsertRoute() async {
+  void dbInsert() async {
     Database database = DbHelper.db;
     id = await database.insert(
       "route",
@@ -295,7 +295,7 @@ class Station {
     """);
   }
 
-  void dbInsertStation() async {
+  void dbInsert() async {
     Database database = DbHelper.db;
     database.insert(tableName, toMap());
   }