altering notebook template to prevent nbviewer logo failure
readding target blank
more technically correct html/css handling of this issue
Merge branch 'master' into fix_nbviewer
per discussion, text fallback not needed
Merge branch 'master' into fix_nbviewer
Merge pull request #811 from ContinuumIO/fix_nbviewer

Fixes Bokeh Logo repetition in nbviewer notebooks.