what's new tweaks

update nbconvert command-line call and add a few links.
Added explicit error message for missing configuration arguments.
noteboook with spaces.ipynb test
updated test for spaces in filename
use notebook which has an image in it for the test
use grffile to support notebooks with spaces
add grffile to the basic latex template
move raw_input / %debug to higher prominence

in what's new
Merge pull request #3908 from minrk/whatsnew-nbconvert

what's new tweaks
change docs/examples refs to be just examples

this closes #3915
Merge pull request #3917 from ivanov/fix-3915

change docs/examples refs to be just examples

closes #3915
added check_for_tornado, closes #3916

This way, those relying on the output of `python setup.py install` get
clued in about the fact that it is required for the notebook
Merge pull request #3918 from ivanov/fix-3916

added check_for_tornado

closes #3916
Merge pull request #3913 from ivanov/alt-fix-3774

use grffile to support spaces in notebook names

closes #3774
closes #3898
Merge pull request #3910 from dhirschfeld/config-error

Added explicit error message for bad connection files.