Add api support for user selectable columns
One of the desirable UI RFEs is to have support for "user selectable" columns. For example on pages like host list or organizations list a particular user might want to only see the list of organization labels and not care about the rest of the columns. The user would want this information stored and the future visits to that same page should get rendered based on what the user chose.
To this effect we need to facilitate a data model + api controllers so that plugins like Katello can make use of this .