Issues/1987 autolayout breakage

Fixes #1987 
Moves the reader detail content out of a cell and into a table header view.  Avoids competition between baked in cell animation and when DTAttributedTextContentView invalidates its content size. 

cc @jleandroperez for autolayout interests and @drw158 for the related issue in #1988 (which should also be fixed with this.)