User ID is NULLable now results in expected tests results: nb_users = 0 when no user id was set. refs #3490 #6162

refs #3490 Throw meaningful error when userId segment is used with an unsupported segment match operator + test

fixes #5933  New $period parameter to the API call CoreAdminHome.invalidateArchivedReports refs #6116

Refs #6078, order pivot table columns by sum, descending and aggregate cut-off columns into 'Others' column.

Make sure PivotByDimension respects original segment query parameter when fetching intersected tables by segment.

Adding new PivotByDimension DataTable filter that can pivot a report by (almost) any dimension. The filter can pivot reports by their subtable dimension and can also pivot by other dimensions (by using segments).

Notes:

- in the UI, only pivoting by subtable is supported
- change to CSV DataTable renderer so column names w/ commas & quotes can appear in text
- change to XML DataTable renderer so column names w/ invalid XML characters can be rendered (bit of an iffy change, XML format needs an overhaul I think)
- includes new config option 'pivot_by_filter_enable_fetch_by_segment'
- includes additions to component metadata classes (ie, Report/Dimension)

refs #4996 redirect only to trusted hosts (will have to remove this most likely again as you would have to register subdomains etc as well). Also added some missing test files

Added tests for segments, renamed fixtures, removed code duplication, changed purge invaldiated data task priority

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

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