Add 'Back to search results...' button after a search has been conducted.

[bluewomble]

If I search my mail and the search brings back many results and then open one of the results, I'd like to have a button that takes me back to the search results.

In case the above is not clear, here is an example:

1. I want to find a mail from some time ago, so I search for a word or phrase I think will be in the mail.
2. Wait for search to complete
3. I get 30 search results back. Unfortunately, I can't tell just from the sender, date and subject which is the mail I want... I'll need to open them
4. I open one of the mails (with a double-click), unfortunately that isn't the one I wanted.

At the moment, once I have reached stage 4, I have no way of _quickly_ getting back to stage 3 (i.e. the results window.), I have to repeat all the steps 1 to 4 again (and I have to wait for the search to complete again)

I propose that a 'Back to search results' button should be added once I have conducted a search to take me back to my previous results, this would quickly jump back to stage 3 above.

[thomasb]

Actually a duplicate of #1483883