Scan display refactoring
To do:
- in a separate application, listen scan data from redis and display scan in console
- console is to be displayed in another ptpython buffer
- filter scan events to only show the current process scan
- the basic scans are known to the display function
- user can define his own display function
code can be written in bliss.data.display module
- scan api : keep data watch callback kwarg
- think about the progress bar