Refactor TiffSaver.isAlreadySaved -> findSavedScan.
Refactor TiffSaver.isAlreadySaved -> findSavedScan.

Add TiffSaver.listtiffs method.
Implement flexible scan specifications - by list, integer, slice, etc.

NSLS-II-XPD/ipython_ophyd,pavoljuhas/ipython_ophyd,pavoljuhas/ipython_ophyd,NSLS-II-XPD/ipython_ophyd