trigger `Kernel.status_started` after websockets open

This leads to a more logical state for event watchers to expect.
remove special handling of speaker notes
clarify `reveal-prefix` alias name
update nbconvert docs about reveal.js
add proxying tornado server in Serve post-processor
use local reveal.js url prefix by default

CDN redirect is handled by the Serve post-processor if necessary
add missing data_javascript

Note that javascript is still excluded from html output by default.

candidate for backport to 1.1
minor adjustments to markdown / rst templates

- remote prompts from output
- add missing HTML block
- remove double-wrapping of latex
- use plain-markdown indentation for code blocks (could use GFM '` ` `python')

closes #4024

candidate for backport to 1.1
fix markdown images

use split-files for embedded images

add path2url
fix jpg/jpeg type in sphinx
fix skeleton template makefile
run skeleton template makefile
Merge pull request #4178 from minrk/data_javascript

add missing data_javascript
Merge pull request #4174 from minrk/markup-templates

various issues in markdown and rst templates

- remove prompts from default output
- add missing HTML block
- remove double-wrapping of latex
- use plain-markdown indentation for code blocks (could use GFM ``` ` ` `python```)
- images didn't work in either one at all
- markdown extracts output

closes #4024
converted multi-context with-statements to nested (2.6 compatibility)
moved DummyMod to proper namespace to enable pickling
Revert "converted multi-context with-statements to nested (2.6 compatibility)"

This reverts commit 311acdf45e9d164ac3dd3eb72b913dfc7d7e4314.
always fire LOCAL_IPS.extend(PUBLIC_IPS)

was in `else`, but should have been `finally` so it aways runs.


Symptom was warnings in parallel.client about `127.0.1.1` not being this machine.
update version-check message in setup.py and IPython.__init__

clearer message that IPython no longer supports 2.6.
update Python version classifiers:

- drop specific 3.x
- drop 2.6