Refactor Statsd classes to enable null collector to work.

Refactor Statsd classes to enable null collector to work.

The following changes are added:
- Created MediawikiStatsdDataFactory interface
- Added hasData() method to see if there are any data to send
- Added getData() method to fetch data
- Made service infrastructure use MediawikiStatsdDataFactory interface
- Made wfLogProfilingData() use MediawikiStatsdDataFactory interface
- Added capability to enable/disable buffering collector

Bug: T166354
Change-Id: I2874175647e987996a9a399829b3319674471aaa