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
create new terminals with POST /api/terminals

instead of GET terminals/new

to be consistent with creating new notebooks.

We had to stop using GET notebooks/new
because browsers would create new notebooks when making preview thumbnails for commonly visited pages, etc.
I assume the same issue would apply to terminals
upate exmaple notebooks to nbformat v4
Make a window immediately, and set its location on response

Avoids the need for async:false
Close new window on error creating terminal
DEV: Support for configurable list of extra jinja template directories.
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.
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
Merge pull request #6873 from takluyver/contents-api-no-dialog

JS Contents API doesn't need dialog module