Tracking API: allow bulk tracking without token_auth

[mattab]

The goal of this ticket is to allow bulk tracking without token_auth. Follows up: #4994.

Tasks:

• Create config setting to require token_auth when using bulk tracking
• Update test to not set the token_auth when bulk tracking
• Update http://developer.piwik.org/api-reference/tracking-api

This will also fix: #5010

[mattab]

In 2acb364: Fixes #5030 Tracking API now does not require token_auth for bulk requests.
To make behavior the same as in Piwik 2.1.0 or earlier, set the following config setting under [Tracker]:
; Whether Bulk tracking requests to the Tracking API requires the token_auth to be set.
bulk_requests_require_authentication = 1

[mattab]

Todo:

• Update doc: http://developer.piwik.org/api-reference/tracking-api#bulk-tracking

refs #4994

[mattab]

In a317e32: Refs #5030 Modify test

[mattab]

Bulk tracking documentation is updated