adjustments to nb_roundtrip.js

A few waits, little changes to get it running with recent changes
update shutdown_notebook

now that get_output_cell raises if there is no such output
move signature checking to base NotebookManager

so that subclasses have less to duplicate
Python 3 renamed hashlib.algorithms to algorithms_guaranteed
add `ipython trust --reset
add notebook signing docs
Improve description of Qt console embedding options
Merge pull request #4849 from minrk/unicode-is-the-devil

Various unicode fixes (mostly on Windows)
Fix some doc formatting in pandoc checks.
use importlib.machinery when available

avoids deprecation warning on startup, and allows tests to pass with PYTHONWARNINGS=d

closes #4051

candidate for backport to 1.2
Fix some formatting in widget docstrings
Remove the docscrape modules, which are part of numpydoc
More minor doc fixes.
Merge pull request #4949 from takluyver/remove-docscrape

Remove the docscrape modules, which are part of numpydoc
Merge pull request #4928 from minrk/suffixes

use importlib.machinery when available
Properly set uploaded notebook path.
Merge pull request #4927 from minrk/no-files-prefix

there shouldn't be a 'files/' prefix in FileLink[s]
Tiny comment correction
Reset file upload form after an upload.
Merge pull request #4950 from ellisonbg/file-upload

Two fixes for file upload related bugs

closes #4825
closes #4871