Add tool for image problem validation/checking

[sosey]

Create a tool in the wfc3tools package that users can examine their data with - basically do a header keyword check on the files to alert users to problems that might have occured with the data.
For example: Now that TDFTRANS is ignored, check this key in the imsets for IR data and alert
Get a list of other important keys from the group, consider letting users supply their own list.