update pylab messages

add `Populating namespace` message to `%pylab`

from @fperez
add `--matplotlib` flag to terminal IPython

just like pylab, but for `enable_matplotlib` instead
unicode fixes in SVG

minidom.parseString doesn't like unicode objects
re-run example notebooks without `%pylab`

prefer `%matplotlib` and explicit imports
update parallel example notebooks to remove `%pylab`
populate matplotlib / pylab enums from backends.keys()
move imports to %pylab description

from no-import-all description, which gets re-wrapped by argparse.
remove quarantine

it's been long enough, and these files can always be found in the git history
make inkscape command configurable

and fix b64 treatment of PDFs
simplify ConvertFiguresTransformer

it will always run *before* extract figures
add pdf to latex display priority
add data_pdf block to latex templates
Merge pull request #3695 from minrk/nbconvert

fix SVG2PDF

there were some logical issues, with SVG2PDF assuming it was run
both before and after figure extraction.

Also makes the inkscape command configurable,
in case it doesn't work some places.

Adds pdf block for output in latex templates.

closes #3693
fix unicode file-writing in svg2pdf
fix exception raising in svg2pdf
tweak inkscape configurability

now you only specify the 'inkscape' path if it's non-default,
rather than re-specifying the whole command (whole command still configurable for non-Inkscape use case).
Merge pull request #3699 from minrk/svgpdfunicode

svg2pdf unicode fix

also tweaks to exceptions and config in svg2pdf

closes #3698
Merge pull request #3686 from minrk/rm-deathrow-quarantine

remove quarantine
Merge pull request #3683 from minrk/matplotlib_magic

use `%matplotlib` in example notebooks

- removes any mention of `%pylab` in our examples
- adds `--matplotlib` command-line flag, mapping to the new
- adds `Populated namespace` message to %pylab output, at the request of @fperez.
- fix unicode bug in SVG, discovered during testing

closes #3680
closes #3684
Merge remote-tracking branch 'upstream/master'