Set "title" attribute for images from markdown

It’d be nice if we could set the title attribute for images as well as the alt attribute with the caption being entered in the markdown.

[halfdan]

Regarding the title: I propose to use

<figure>
  <img src=".." alt=".." title="Optional title" />
  <figcaption>Optional title</figcaption>
</figure>

This would make it easy to add captions to images that are easy to style with CSS.

@JohnONolan This isn’t a Markdown extension. It’s part of the original Markdown: http://daringfireball.net/projects/markdown/syntax#img

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I’d like to implement this if above format is accepted.

[ErisDS]

Closing as wontfix against #1294 as it’s pretty hard to get done before we rebuild the editor.