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
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