Parse the style*.xml file in the OOXML package, and store the imported styles in XChartDocument via a new XChartStyle. Some areas are yet to be fleshed out, but the intent here is to get a review of the general approach and architecture. This includes no work on the export side (or the UI and application of styles to a chart, which is a separate but related project). Change-Id: I9d5b9f5aa44fb7944b2d971edc26e04dc2256c7f Reviewed-on: https://gerrit.libreoffice.org/c/core/+/189531 Tested-by: Jenkins Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>