Scan progress with ptpython

This PR rework the scan progress to display it as a ptpython application.

• The execution of the scan progress was moved from Scan to ScanProgress.exec_context
• exec_context was then reworked to support optionally TextBlock
• The implementor have to enable it explicitly for now (in order to have time to convert stuffs from the beamlines)
  • See USE_TEXTBLOCK = True setup by the StepScanProgress
• When USE_TEXTBLOCK = True
  • The ScanProcess implementation must not print anymore stuff
  • The function progress_task is not anymore called
  • The function build_progress_message have to be implemented
• Also build_progress_message is called before the preparation of the scan, at this stage every metadata from the scan info are not yet there
• Limatake progress and StepScanProgress was converted