Refs #7830 - Add extra doc and console messages.

Attempt to make it more clear in the console output what is going on and
why.
Refs #7830 - Check for existance of cURL.

Stop script if we can't use cURL.
Refs #7830 - Add DOIs to welcome message.

Hopefully it's the right patch number from CMake - need to double check
this.

Nick needs to confirm the exact wording of the message, as well as the
"desciption" field in the DOI metadata.
Refs #7830 - Simplify release DOI generation.

Being defensive by using lexical_cast is not necessary, and is not even
done elsewhere in the file.
Refs #7830 - Use simpler test for cURL.
Refs #7830 - Improve deleting of DOI's.
Refs #7830 - Use different Cmake variable.

This takes into account Martyn's changes on #8097, which should be merged
into this branch from master once his ticket has passed testing.
Merge branch 'master' into feature/7830_doi_messages_on_startup
Refs #7830 - Add names to whitelist.  Change metadata slightly.

Whitelisted people now appear ONLY in the "main" DOI.  Names scraped from
Git will be included in both the main DOI and the relevant incremental
"release" DOIs.
Refs #7830 - Tidy up About window.
Merge branch 'master' into feature/7830_doi_messages_on_startup
Refs #7830 - Generate only one DOI.

On a major/minor/patch build the DOI will point to release notes, and on
dev builds the DOI will point to the main mantidproject.org web page.

Updated report log to show this single DOI, and added it to the About
window too.
Merge branch 'feature/7830_doi_messages_on_startup' into develop