"Extract image…" makes images linked relative to one's home directly instead of where the SVG is located

[Garrett]

How to reproduce:

1) Right click on an embedded image
2) Select "Extract image…"
3) Enter a relative path and/or name
4) Select "Apply"
5) The file appears in your home directory, unless you specified a path that doesn't exist.

Here's what I expect:

* An embedded image should become linked relative to where the SVG exists
* If the directory (such as "assets") doesn't exist, create it

[jazzynico (jazzynico)]

> An embedded image should become linked relative to where the SVG exists

Confirmed. Except when the file was not saved before and thus doesn't exist in a path. In that case, we could keep the current behavior.

[jazzynico (jazzynico)]

Unfortunately, since we dropped the document absolute path (for security reasons), there's no way for the extension system to know the document's path (extensions use a copy in a temporary file, not the document directly).