SMW\SQLStore\StatisticsCollector

Test coverage: 100%
CRAP: 21

* Move statistics into its own StatisticsCollector class to ensure
proper test environment
* SMWSQLStore3::getStatistics only returns results from
StatisticsCollector::doCollect()
* Add profiling point for each count statistic
* Add caching for statistics results using $smwgStatisticsCache and
$smwgStatisticsCacheExpiry settings

## Default settings
$smwgStatisticsCache = true
$smwgStatisticsCacheExpiry = 3600 // 1h

Change-Id: Id189dd17c7e2591764896baf6e344b4590ca65e4
Merge "SMW\SQLStore\StatisticsCollector"