Refs #3490 User ID Tracker is now working:
- new user_id field to contain the raw user id value
- new &uid= tracker api parameter
- add userId to Live API output
- added integration test
Refs #3490 User ID Tracking with Piwik.js + tests
Refs #3490 Encode user id value before sending to Tracking API.
refs  #5995 Remove xhprof, and other phpunit dependencies, from the vendors to keep builds light
Refs #6109 cid should not require token_auth authentication. Note; this may fail the test with changes in Tracker.php
Refs #3490 Adding segment 'userId==' + some '&segment=userId==' integration tests + doc blocks
Refs #3490 Displaying User ID in the Visitor log
Refs #3490 Displaying User ID in the Visitor log
Refs #3490 hide user_id attribute from Live API responses when requesting user is anonymous
Refs #3490 Display User ID in the Visitor Profile, in the Visitor log and Last visits widget link/tooltip opening the Visitor profile
Refs #6109 update docs
Merge branch 'master' into 3490_user_id

Conflicts:
	core/Version.php
	misc/package/build.sh
Refs #6109 New core metric: nb_users as the count of distinct user ids. Means "Active Users". Displayed in Visitors Overview, in metrics picker, in API response, in Metadata
Refs #3490 Docs, and fix a few tests, more to come
Fix plugin tests
refs #6162 when aggregating periods, do not sum 'Unique Users' metric as this is not a valid operation.
refs #6162 do not display nb_users in all reports within Scheduled reports + fix some tests
fix some tests
refs #6162 Fix a bug / copy paste fail
refs #6162 Fix tests after adding nb_users