Prepare version 2.7.2
Simplify default arguments.

Default arguments get evaluated once when program begins. Not when the
function is called. As such value may be obsolete by time function
is called. Fixed.
Remove database initialization for machine_category.

No need to initialize machine_categor in management.py
(5acdf701e65e6451b24b4c3bf8d798ba2792bc38), as
it is done in karaage/machines/sql/machinecategory.sql

This change now works as a result of
d52d2c6f00e0beb9fe0bd31b12de23194bd6caac
Fix broken link.