Introduce a setting to change the display format of timespans to h:mm (#23996).

Patch by Jens Kraemer.

git-svn-id: http://svn.redmine.org/redmine/trunk@15965 e93f8b46-1217-0410-a6f0-8f06a7374b81

config/settings.yml

@@ -153,6 +153,8 @@ date_format:
   default: ''
 time_format:
   default: ''
+timespan_format:
+  default: 'decimal'
 user_format:
   default: :firstname_lastname
   format: symbol