Export Nexus integrated curves to multiple ASCII files

This MR aims at addressing a request from ID31 to export integrated curves to ASCII files from xrpd_processor.

As it is, the added task is meant to be plugged to IntegrateBlissScan. It reads back the NXData group (with retry I expect) to export as ASCII files. It is a bit flexible and supports 1D and 2D signal. IMO it can be generalized to NXdata to ASCII files.

A simpler alternative is to extend the IntegrateBlissScan task with an optional save as ASCII feature (See example here: 5c24dee4). This would also simplify the management of workflow in the xrdp_processor since there is no change in the workflow with/without ascii export.