Incremental improvements on the IPython-based control system

[Jasonzhouquan]

This PR is to address the issue layout in #8 and #9. Details are listed below:

• Improved sorting of imports.
• Deleted function getRunEngine (Default databroker -> mongodb).
• Improved function hutch_light_on as suggested.
• Added print_RE_md() and show_ophyd_symbols() as suggested.