gradual improvement

[KedoKudo]

Several key changes were introduced in this PR (tested at 6BM):

• All devices are initialized via functions and set to 'debug' mode by default
• A global switch, mode, is used to toggle between different mode
• Devices staging is bypassed with an empty dictionary
• Fly and step scan are merged into one simple plan
• Motor initial position is cached in a dictionary, and resume motor position is done manually via resume_motors_position()
• Two dictionaries are used to track the predefined functions and vars, hopefully, to alleviate potential namespace contamination issues

Future development targets:

• Robust automated failure recovery
• Auto messaging for status update
• Global reinitialization function(s)

[prjemian]

Consider this (new) shell script to setup the custom bluesky environment:

https://raw.githubusercontent.com/BCDA-APS/use_bluesky/master/python_installation/create_bluesky_env.sh

A document about it is here: https://github.com/BCDA-APS/use_bluesky/tree/master/python_installation