Make special character handling in display function respect a preference, so that it can be turned off

[jegelstaff]

As of 3aff3a3 the display function turns off html special characters in single values returned from the database. This is a step in the right direction. But it can break existing systems if the value returned from the database is used in subsequent queries or filters that lookup stuff in the database (which will have special character in the database, for now).

So it should be possible to turn this behaviour off via a Formulize preference, at least for now. When storage format and API return format are in synch, then this preference would be redundant. But until then, to preserve existing behaviour on existing systems, a preference is important.