Add unit tests for new Metrics Formatter classes and remove existing ones. Small change to Overlay included and bug fixes to metrics formatting code included.

Declares a process as finished as soon as a PID file is > 500bytes
(contains only PID) and output file is > 100MB (which should usually
not be larger than 100KB or 1MB) to prevent files growing up to many
GBs. I added unit and integration tests for the file size detection. It is
now possible to mock the methods file_exists and filesize although very
simple so far. Later we can allow to define callbacks or to define different
return values for different files or we can use something like vfsStream

Moved processed metrics computation to DataTableGenericFilter, removed new filters & implemented as methods in Report to avoid confusion regarding re-use, allow adding processed metrics as DataTable metadata and use this to rewrite AddProcessedMetrics filter, correct name of Metrics::getMappingFromIdToName function, added placeholder AggregatedMetric class for future, revise Metric/ProcessedMetric hierarchy (add methods for translation/etc.), allow .get API methods to use metadata to automatically figure out which columns to select, get EcommerceOrderWithItemsTest to pass.

refs #6481 in report generator always show the dimensions of the selected plugin even if the plugin is not enabled

Fixed getCurrentUrl() and getCurrentUrlWithoutQueryString() + tests

Note that I still do not understand how this could be triggered, hopefully if we log we will gather more info about issue.