SMW\SQLStore\PropertiesCollector

SMWPropertiesPage
Code coverage: 100%
CRAP: 21 (before 420)

SMW\SQLStore\PropertiesCollector
Code coverage: 100%
CRAP 12

Final act in moving things out of SMWSQLStore3SpecialPageHandlers and
make it truly testable.

Collector has morphed itself into full inheritance class therefore move
duplicate stuff from sub-class into the abstract class.

## Settings

* Add $smwgPropertiesCache
* Add $smwgPropertiesCacheExpiry
* Add $smwgPropertyLowUsageThreshold specifies the value for when to delare
low usage
* Add $smwgPropertyZeroCountDisplay specifies if properties with 0
usage should be listed as well

Change-Id: I348a553f92eb249225c5f67115e7264eb8cc49ab