Fixes #6756, fix two regressions/bugs in row evolution of ecommerce item report: viewDataTable is overwritten by BaseEcommerceItem Report class metadata causing UI bugs since viewDataTable is not graphEvolution, graph visualizations should not format metrics in any way prior to generating jqplot JSON.

Refs #6109 New core metric: nb_users as the count of distinct user ids. Means "Active Users". Displayed in Visitors Overview, in metrics picker, in API response, in Metadata

Piwik is a free/libre analytics platform. Refs #4455 GNU Package requirement to use free/libre instead of open source

using phpstorm optimize imports feature

using phpstorm optimize imports feature

fixes #4609

Fix regression in metrics picker: remove available column check. Use of 'columns' query parameter in API methods makes this check problematic.

renamed configureVisualization to beforeRender and trigger it at after filters are applied. makes it easier to understand that this hook is meant to force the value of some config properties. this change probably breaks some features, will fix it then

define client side and overridable properties in config, not sure if it is a good idea but we will see

adjusted some visualizations to the new viewdatatable structure, the platform is displaying some data again

added interface for dataTable to be able to define the expected type in a function, maybe it makes sense to add/remove some methods from the interface?

trying to use some hooks for visualization, properties are now handled in request/view data objects without any logic, not sure if it works, still an experiment, probably does not work for custom visualization properties

Moved/renamed DataTableVisualization to ViewDataTable\Visualization and moved Graph to ViewDataTable\.

Refs #4041, #3317, allow visualization ID to be whole class name, allow footer icons to be customized per report/visualization, made visitor log a new visualization and removed the datatable_template display property.

Refs #4041, force DataTable visualizations to specify which properties should be overridable and move some view properties to different visualizations.