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

remove the read noise terms (first add to then minus from base image) from possion noise generation.

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