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
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
Merge pull request #6835 from minrk/travis-pip

expedite installation on travis
use slimerjs on travis

because phantoms doesn't work with tornado < 4