Added more server and php section to info being tracked

Also:
- Added db_charset to the site variables being monitored
- Moved the server/php specific variables out of the WPSEO specific section to the more generic section as independently of which plugin is using the tracking class, this info is interesting
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Tracking-additions
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Tracking-additions

Conflicts:
	admin/class-tracking.php
[Temporarily] Moved the new tracking info to the WPSEO options section
Merge pull request #1232 from jrfnl/Tracking-additions

Added server and php section to info being tracked