Cells with 'bool' profile not printed with default printer settings

[sammakkoinen]

Columns with 'bool' profile use CSS background-image to display values (checked/unchecked mark). However, at least with 2 different printers and 3 browsers I have found that the default setting is "Not to print background graphics". This can confuse users who won't get checkbox values printed, and the reason (printer settings) is hard to determine. As checkbox values are content, not presentation, I suppose CSS background images aren't suitable here. (The issue could be fixed by changing the 'bool' profile and/or code in RA::Module::Datstor::Column, but I haven't found a way to modify/add my own custom profiles and would like to avoid modifying/subclassing Datstor::Column if other ways are possible.)