Conflicts:
	core/Metrics.php
	js/piwik.js
	piwik.js
	tests/javascript/index.php

refs #4996 many new tests and many bugfixes. Tests should be done now except for cross browser support. I fixed many issues as I did not consider that link tracking may be disabled or enabled and the behavior should be different in such a case.

Fixes #5923, add INI config option allow_adding_segments_for_all_websites that allows users to disable the ability to add segments affecting all websites.

refs #4996 it should basically work but need todo some more stuff like cross browser and php tests. A few more minor and easy to implement features as well

Fix Transitions UI test (don't use id attribute to check if row has subtable, use subDataTable class).

refs #4996 more bugfixes, more work on cross browser, added possibility to track content via php tracker (not tested yet)

Refs #5355, use existing plus/minus icons in normal subtable reports and don't use new CSS for actions reports which use images.

Fixes #6079, move skip unique visitors calculation logic to small method in ArchiveProcessor\Rules and fix build.

Allow LogAggregator to work with multiple site IDs, compute unique visitors for archives of multiple sites and add option to control whether unique visitors for multiple sites are processed.

Fixes #6178, select columns of a table correctly in handleColumnHighlighting function in dataTable.js.

Fixes #5355, add plus/minus icons to left of rows w/ subtables that change when tables expand/contract. Also add tooltip to rows w/ subtables.

Fixes #6034, replace down arrow in segment selector top control with icon used in segment editor. Also fixed issue where selector size change would not move icon to the right.

Testing if /proc is a resource with @fopen fails on systems with open_basedir set.
 by using stat we not only test the existance of /proc but also confirm it's a 'proc' filesystem

refs #4996 many new tests and bugfixes, worked around some JSLint regexp issues and disabled the whitespace check which makes no sense to me. The tests do now run again in PhantomJS but report a lot of failures and I have not looked yet into it.

User ID implementation 

new "Users" metric in graph picker https://github.com/piwik/piwik/issues/6162, JS code showing //host notation https://github.com/piwik/piwik/pull/344  adding optout iframe screenshot

fixing few more tests: hide nb_users to make tests pass because for some reason the column does appear by default but in the backwardsCompatibilityTest it does not appear there. Also had to manually activate and install plugins in the test case for some reason. Message was:
```
Exception: Failed to update database (errors or warnings found): Array
(
    [warnings] => Array
        (
        )

    [errors] => Array
        (
            [0] => /home/matt/dev/piwik-master/plugins/CustomAlerts/Updates/0.0.2.php:
Error trying to execute the query 'ALTER TABLE `alert` CHANGE `enable_mail` `email_me` BOOLEAN NOT NULL'.
The error was: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'piwik_tests.alert' doesn't exist
        )

    [coreError] =>
    [deactivatedPlugins] => Array
        (
            [0] => CustomAlerts
        )

)

```

and restore Transitions tests which I deleted by mistake earlier

refs #6162 Extending config setting enable_processing_unique_visitors_* to also affect the nb_uniq_users metric processing over periods, + only show Users metrics when it's greater than zero, + fix more tests and renamed test suite to UserIdAndVisitorIdTest