Expose gradient norm clipping to the command line.
Expose gradient norm clipping to the command line.

slai11/youtube-8m,slai11/youtube-8m,hxkk/u8m_test,lidalei/youtube-8m,KangHsi/youtube-8m,coded5282/youtube-8m,slai11/youtube-8m,forwchen/yt8m,forwchen/yt8m,slai11/youtube-8m,KangHsi/youtube-8m,google/youtube-8m,mwoodson1/youtube-8m-competition