If Piwik is not installed yet, it's possible the tmp/ folder is not writable, display a useful error message

If Piwik is not installed yet, it's possible the tmp/ folder is not writable
we prevent failing with an unclear message eg. coming from doctrine-cache
by forcing to use a cache backend which always works ie. array

* Renamed plugin ExampleRssWidget -> RssWidget

* Activate file on upgrade to 3.0.0-b1

* Fix system test

Extract the first IP from HTTP_X_FORWARDED_FOR  and HTTP_CLIENT_IP and HTTP_CF_CONNECTING_IP and HTTP_X_FORWARDED_HOST when there is more than one IP (#10404)

* Extract the first IP from HTTP_X_FORWARDED_FOR when there is more than one
Fixes #10342

* Fetch the first IP from a list of IPs

* Return the first non empty IP

refs #6106

Professional Services for Piwik - neutral branding within Piwik app

Signed-off-by: Stefan Weil <sw@weilnetz.de>

* Implement the UserId module, that adds a new Users report showing all unique user IDs and some aggregated data. Includes reindexing of raw visitors log into aggregated user ids table

* Update UserId module: add total_actions, total_events and total_searches columns; format dates

* Use an injected model instead of creating a new object

* Rework the UserId plugin to use core archiver instead of custom indexer

* Users report small changes:
- remove logger injection
- change archive record name
- add low population filter
- add all columns visualization
- add datatable_archiving_maximum_rows_userid_users configuration, default value is 50000

* Remove unused method parameter

* Users report: remove custom visualizations and add data-row-metadata attribute for every row

Rename whitelist to blacklist since we're ignoring entries that are in the list, not running code only for those entries.

Instead of hardcoding whitelisting of Overlay methods in UI test URL normalizing, use DI to store whitelist and override in ui-test.php DI config for Overlay.

Remove host & port only if test port is defined in config & remove Piwik base path from all output so tests won't change based on machine.

Allow extra environments to be specified through testing environment variables, add a new one for UI tests call ui-test.php, use to remove port from localhost in UI tests, and fix a bug in ContainerFactory (config/config.php should be applied after environment files).

Try to fix nginx setup on travis. Includes new [tests] INI config parameter for port (since using port 80 is not allowed for normal users on linux).