#5 Whisker plots

This pull request is for adding a functionality of generating whisker plots. It includes the following things.

1) A `WhiskerPlotSysTest` class in `sys_tests.py`, which is a base class inherited by specific whisker plot classes for three quantitates (g1, g2, and sigma), i.e., 3 classes whose names are `WhiskerPlot[Star,PSF,Residual]SysTest`.

2) An interface to the HSC pipeline is added in `hsc/sys_test_adapters.py`. Each test can be run by adding `WhiskerPlotStar`, `WhiskerPlotPSF`, `WhiskerPlotResidual` to a list `sys_test` in the config. Examples of a command line are as follows
- single CCD
```
StileCCD.py $SUPRIME_DATA_DIR --id visit=1228 ccd=49 --rerun [rerun_name]:[stile_rerun_name] --clobber-config -c "sys_tests.names=['WhiskerPlotStar', 'WhiskerPlotPSF', 'WhiskerPlotResidual']"
```
- multiple CCDs
```
StileVisit.py $SUPRIME_DATA_DIR --id visit=1228 ccd=004^009^090^095 --rerun [rerun_name]:[stile_rerun_name] --clobber-config -c "sys_tests.names=['WhiskerPlotStar', 'WhiskerPlotPSF', 'WhiskerPlotResidual']"
```
. A bunch of options are added in `hsc/base_tasks.py`. For getting (x, y) coordinates on a focal plane in the multiple CCD case, a functionality of getting zero point of (x,y) is added to `base_task.py`.
Hmm, interesting--thanks for this fix.