Add `viewable` field to Concept preserialize template
Add `viewable` field to Concept preserialize template

This bug was originally seen in cbmi/avocado#155. The client evaluates the
presence of `viewable` or `formatter_name` to determine if it should appear
in the columns dialog. Because `viewable` was not present, concepts using
the default (falsy) formatter would not appear.

chop-dbhi/serrano,rv816/serrano_night,chop-dbhi/serrano,rv816/serrano_night