Add support for Sundials 5.0.0 & and update submodule version

[speth]

• There is a clear use-case for this code change
• The commit message has a short title & references relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage

System installations of Sundials 5.0.0 work without any internal changes to Cantera. Some changes to the build system are required to use it from the git submodule, which is also updated here to point to the official LLNL repository.

[bryanwweber]

With this change merged, I had to perform the following steps to update my local master branch. I'm not sure if this is totally necessary, but it worked for me. A simple git pull upstream master resulted in

Fetching submodule ext/sundials
error: Server does not allow request for unadvertised object 38aa03b990e616db52acd053730c31fcc3eb91f9

This was because the ext/sundials submodule didn't automatically update the remote. Running git pull upstream master again pulled in the changes to all the files in Cantera, and then git submodule update --recursive resulted in the same error message. So I had to

cd ext/sundials
git remote set-url origin https://github.com/LLNL/sundials
cd ../..
git submodule update --recursive

and then everything was up-to-date. Just recording this here so we can either give advice in the release notes or respond to issues on the UG.