Feature Request: Document-relative image paths for Insert Image dialog

[transplier]

Right now, images embedded via the dialog use absolute paths. This messes things up if, for instance, the markdown document and images are viewed from a backup folder, or I rename my work directory, or I view the document from another computer.

Of course, relative paths are not always ideal. It would be nice to i.e. have a checkbox on the Insert Image to optionally embed relative. Of course, this checkbox would have to be disabled (ideally with a user-visible explanation) if the current document has no file name (because document-relative paths have no meaning without a document file).

Save-as gets a little tricky - it would be nice to warn the user if the document with relative paths is being saved into a different directory. Super extra bonus points if the files are then copied.

[borghal]

Second that! Even though preview is working with relative paths, pdf export fails to insert the images. Please include relative paths for images in pdf export.