issue17:fix led model memory bug; issue19:header time is not utc bug; issue18:header data-obs\darktime\exposure time fix by shaoli's chart;add new star catalog:C6_50sqdeg_ns.py

* Changed the name of output folder of pointing to corresponding pointing.obs_id.
* fixed the order .cat hdr updating and the creation of .cat file.
* Changed the naming of shutter and flat reference image: chip IDs now all in 2 digits.
* Updated the __init__ method of ChipOutput
* Removed Config.py from ObservationSim.Config
* Cleaned codes in ObservationSim.py, ChipOutput

remove pointing_dir, data_dir in overall_config

1.Modify fits header by defination;2.fix fgs bug: whether shutter effect open or close, fgs run error; 3. read pointinglist bug: jump the data of first row

1. add project_cycle, run_counter to config file. Modified obsid to reflect this change. Applied the same obsid to ".cat" and ".log" files.
2. limiting mags are now based on the field types (WIDE or DEEP) which can be specified in pointing list.
3. Stars are now drawn directly as PSF.
4. Reorgnaized lists of filter types in Instrument._util.

1. Update the field distortion models for FGS detectors (with new wcs definition). 2. Update README.md

rotate e1, e2.
remove the rotation parameter in Galaxy class (not used before).
modeling of ellpiticity rotation should be implemented in Catalog.py