piwik_stats 7.x-2.0-beta2

This is a general rewrite of the 7.x-2.0-beta1.
Improved stability, usability and ease to scale on large sites.

Huge thanks for helping with this release to erikseifert of http://www.b-connect.de!

- Using Cron-queue and Batch-API for filling and pulling the fields (#1386406: Queued processing).
- Fixed bug that caused dropping images when fields are filled (#1666006: Piwik Stats drop image fields).
- Removed many small worst-usage-case bugs.
- Improved UI for fields (unnecessary stuff removed).
- Improved code for making it much easier to maintain.

Cache-Clear required after update!