Allow links in columns

[mrjones-plip]

While the first column in tableManager is always linked to the edit URL, we should extend tableManager to allow subsequent, non-empty columns to be linked to a URL of the developers choosing.

This would be nice, for example, if you had an integer that was the the ID of an object on another web site. If you could set something like $tableManager->setFieldLink('https://site.com/id/', 'column_name_here' so that when we called getHtmlFromRows() (which in turn calls getHtmlRowsBody()) it did the right thing!