use `pip install .[all]` on travis

can't actually use `.[all]` syntax, instead using `file://$PWD`,
but the principal is the same.

get wheels from minrk/travis-wheels to expedite installation
remove timings in travis.yml

Travis does its own timing now
add 'requests' as test dependency

since it is one
upate exmaple notebooks to nbformat v4
distinguish capture_output from buffer_output

allow capturing output without silencing it,
which is useful for slimerjs,
which requires looking at output to determine failure.
DEV: Support for configurable list of extra jinja template directories.
Merge pull request #6860 from minrk/slimerjs

distinguish capture_output from buffer_output
DEV: Add IPython.html to the default template path.

This makes it possible to override a file with a template that also
inherits from that file.

For example, this makes it possible to override a single block of
notebook.html by creating a file called notebook.html that inherits from
templates/notebook.html.
Update components to codemirror 4.7
Merge pull request #6865 from takluyver/cm4.7

Update components to codemirror 4.7
allow multiple forms of latex math in test_markdown

different versions of pandoc use different escapes
Merge pull request #6863 from minrk/markdown-tex-math

allow multiple forms of latex math in test_markdown
upgrading >v4 header cells to unicode

adding test
more human-readable unicode chars in test
Merge pull request #6868 from bollwyvl/unicode-upgrade-headers

upgrading >v4 header cells to unicode
fix unicode literal in v4.test_convert

caused failure on Python 2 on Windows

because unicode!
Merge pull request #6870 from minrk/unicode-literal-fix

fix unicode literal in v4.test_convert
DOC: Fix typo in comment.
Merge pull request #6835 from minrk/travis-pip

expedite installation on travis
JS Contents API doesn't need dialog module