Remove default for when changing custom field format.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11397 e93f8b46-1217-0410-a6f0-8f06a7374b81
Adds the date picker for the default value of date custom fields.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11398 e93f8b46-1217-0410-a6f0-8f06a7374b81