[SERVINF-138] Allow download of list results.

Replicate the download button for all results, even lists.
Readability updates for results_controller.

Prior to real updates. This changes no functionality.
Add licence/comment to run_result partial.

I forgot it earlier.
Use GET for downloading run results.

This was using POST, which is slightly odd for something that is only retrieving
data. GET is appropriate.
[SERVINF-69] Fix results download names.

Result downloads are not all called "value" now and have the correct file
extension too.
[SERVINF-140] Don't assume image type for non-text results.

If the result was not either some sort of text or an error it was assumed to be
an image. This breaks things like PDFs, etc.

Now an image type is explicitly tested for and the catch-all case is a message
to suggest downloading instead.
[SERVINF-100] Show PDF results inline.

It is now set up so that the browser can attempt to show a PDF inline (if it has
the necessary plugin, etc). A message is also shown to suggest manual download
incase this does not work (due to dodgy PDF, plugin, etc).