Send headers with context menu download

[Mayzie]

When right-clicking a link and selecting "Download with Aria2", it should launch the download with the same HTTP headers as the session the context menu is activated from.

This is needed to support downloads utilising HTTP authorisation fields.

[RossWang]

This Add-on interrupts and records the web request that Firefox sends, so it cannot get the headers from context menu which Firefox doesn't send the request.

But if I have time, I will use another way to implement this.

[Mayzie]

Hi Ross,

Thanks for your latest commit!

However, it doesn't handle the Authorization header.

Cheers.

[RossWang]

I am sorry for that. I guessed you were talking about the "cookie" field, but it was not.

In the latest commit, I added the 'Authorization' header support for the auto observer, but it cannot handle the 'Authorization' header for the download request from the context menu because of the reason I talk before.

I have not figured out the good method to handle the 'Authorization' header for the download request from the context menu. If you have any good idea, please tell me.