add screenshot and link into releasenotes

[Carreau]

add notebook tooltip screenshot
add qtconsole ncurses-completer screenshoot

add embeded image of qtconsole completer

I added a tooltip screenshot but didn't linked it into the release notes.

@takluyver
I don't think it is clear in the first paragraph that improved tooltip are only notebook's tooltip

We should also redo the frontpage of the website, that still shows qtconsole without menu, and old leftpannel of the notebook.

[takluyver]

The paragraph about the tooltip is a subheading under the heading about changes to the notebook UI - it's not so obvious in the source, but it's clearer in the output. And when the other notebook changes are described, it should be obvious.

The tab-completer screenshot looks great. For the notebook, I think we'll want to pick a couple of good screenshots as an overview of the changes. @ellisonbg probably has some thoughts on that.

Good point about the website. It needn't be updated yet, but I'll prepare a pull request so that we can easily update it when we make the release.

[fperez]

@Carreau, can you give this one an update as per @takluyver's comments? I can add some more screenshots on the notebook later on, I think the one you have for the tooltip is fine.

[Carreau]

Do you want to keep the same notebooks screenshot as before just with the new interface ?

And I'm not sure to understand the changes I have to change in this PR... @takluyver comment where just things I didn't saw at first in his changes, but I don't see anything to modifie ... Do I misunderstand ?

[takluyver]

The screenshots for the release notes should highlight new features, like the new tooltips, I think.

[Carreau]

added %%octave and %%cython screenshot, tooltip is already here.
I think just giving the link to the screenshots, or have clickable thumbnail is enough as it is not a visual striking feature.
I'll leave @takluyver write in english, otherwise he'll spend as much time correcting me than writing it right.

[takluyver]

Yes, sorry, I meant screenshots for new UI features - the tooltip one looks good, and also shows the new layout with the menu bar. Screenshots for magic commands aren't generally so interesting, unless they're rather visual things (like the %hierarchy magic in a third party extension).

[Carreau]

Ok, removed screenshot of magics,
I re-did the notebook-spectrogram and qtconsole-baboon screenshot.