Rebuild Aevol testing infrastructure

This merge request rebuilds the Aevol testing infrastructure.

• It upgrades the Google Test library to 1.10, using the same hard-copy technique as before.
• It takes all the tests that were scattered around the source tree and puts them inside a test folder at the root.
• It creates a make check target that runs all tests, as well as individual make targets for each test.
• Finally, it makes all those tests pass.