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)