Get processCcd.py working on CFHT images

- Provide working processCcd config file
- Remove cosmic rays from the list of sources used by astrometry.net
- Declare i2 filter to be identical to i filter in astrometry
- Get rid of first astrometry step before psf determination
Fix Megacam mapper for coaddition
Provide default config files for coaddition
Fix amplifier gains in IsrTask
- Adopt CFHT standard amplifier naming convention (A, B instead of 0,0 - 1,0)
- Get amplifier gains, saturation values and readout noise from the input fits headers
Fix bug making ingestImage.py to crash
Answer to code review :
- Initialize self.astrometer in CfhtAstrometryTask::__init__
- Use calibrate.astrometry.solver.filterMap to handle CFHT i2 filter in astrometry
- Remove double specification in config
Do not compress coaddTempExp as NaN are not handled correctly
Remove table version setting according to new versioning scheme
Removed customized astrometry task as the customization is now handled directly in meas_astrom (DM-1057)
Merge branch 'tickets/DM-1380'