add property to better support display remote images with DTAttributedTextCell
add property to better support display remote images with DTAttributedTextCell

Akylas/DTCoreText,rgregg/DTCoreText,Akylas/DTCoreText,Cocoanetics/DTCoreText,Cocoanetics/DTCoreText,pivotaltracker/DTCoreText,Cocoanetics/DTCoreText,rgregg/DTCoreText