Add optional configured CC email address when downloads fail

[ansell]

We need to improve the text of the download error https://github.com/AtlasOfLivingAustralia/biocache-service/issues/246 and 'DOI-failure' https://github.com/AtlasOfLivingAustralia/biocache-service/issues/391 emails.

However, we have no visibility on these at a support level. It would be useful to have an optionally configured CC email in these cases so that support desk personnel can see when things are going wrong with the download and DOI systems and proactively investigate them.

• [x] Add an optional configurable CC email (to support@ala... for example) that defaults to off, but can be turned on by any instance
• [x] Add the configured CC email address to error and 'DOI-failure' emails

[ansell]

The test download failure email you did yesterday was successfully sent to me as a CC. If you push the changes to Git I will code review then it should be good to put through CAB for this series of changes.