Refactor API.getSegmentsMetadata and Plugin\Segment so segments are all defined through Plugin\Segment class in dimensions & make sure AutoSuggestAPITest data providers do not use database.

Make sure format_metrics query parameter is properly handled if supplied to API.getProcessedReport. If not supplied, provide inconsistent but backwards compatible behavior.

Fix regression in API.getProcessedReport, it should not format metrics if showRawMetrics is true. And correctly fdisplay and format avg_time_on_site using processed metric value, instead of recalculating in visitor map.

Make userId segment work for all operators (Is, is not, contains, does not contain, is null, is not null)
fixes #8062
this reverts https://github.com/piwik/piwik/commit/252798d2d742cae998a1f42f50a5ba37c98069df

* Store subtables in chunks of 100 subtables per blob. Those 100 subtables are stored
  serialized as an array: array($subtableID => subtableBlob). The first 100 subtables are
  stored in "chunk_0", the next 100 subtables are stored in "chunk_1", ...
* Subtable Ids are now consecutive from 1 to X
* We do no longer serialize the whole Row instance when archiving, instead we only
  serialize the Row's array which contains columns, metadata and datatable. This is not
  only more efficient but allows us to refactor the Row instance in the future (although
  we will always have to be BC)
* Faster row implementation: Columns, Metadata and Subtables access is much faster now

Keep BC w/ old Formatter class since it is likely used by 3rd party plugins. Move Numeric formatter to CoreVisualizations and do not mark w/ @api.

Fixes #7247, move default Formatter class to new Numeric metrics formatter and use in Graph visualization since jqplot requires numeric values in JSON data.

fixes https://github.com/piwik/piwik/issues/7184

I tested it with 4k websites. The change made it only a couple of seconds faster
but requesting 4k websites would still take 4-8 seconds even if only 10 sites of
them are actually requested. For example before we did request each site 3 times
(12k times in total and triggered 12k events etc) which should be no longer the case.
The last `clearSiteCache` was there to free some memory but I think it shouldn't
be problematic to remove it. Also I removed one 'sort' as a lot of time is wasted
there. It should be in theory sorted afterwards anyway again. Need to see test
results whether this change is good or not.

refs #7075 send correct header if JSONP is used to prevent possible errors in combination with nosniff

plugins/API/Reports/Get.php(70): Warning - array_merge(): Argument 2 is not an array