Add Benchmark tests

Benchmarks tests are using PHPUnit.

- JobQueueBenchmarkTest
- QueryEngineBenchmarkTest
- RebuildDataBenchmarkTest

Group `semantic-mediawiki-benchmark` is generally excluded from unit
testing but doing
`php mw-phpunit-runner.php --group semantic-mediawiki-benchmark` will allow
to run benchmarks individually that are assigned to the
`semantic-mediawiki-benchmark` group.
Merge pull request #512 from SemanticMediaWiki/query-benchmark

Add Benchmark tests