Show tabs for existing custom field types only and adds a view for choosing the type when adding a new custom field.

git-svn-id: http://svn.redmine.org/redmine/trunk@12849 e93f8b46-1217-0410-a6f0-8f06a7374b81
Updated locales.

git-svn-id: http://svn.redmine.org/redmine/trunk@12850 e93f8b46-1217-0410-a6f0-8f06a7374b81