Gain file loading and saving using consistent with vendor header format

[kgofron]

No description provided.

[MarkRivers]

What are you not writing and reading the fileHeader_ structure in a single fwrite() or fread() as is done when reading the bad pixel file?

Why are the fileHeader_ and imageHeader_ structure now member variables, rather than automatic variables?

[brunoseivam]

Also, if the structure was declared as packed, you could probably do:

fwrite((void *) &fileHeader_, sizeof(fileHeader), 1, pOutputFile);

[jwlodek]

We were trying to make the read and write calls be more human readable, which is why we chose to split them into individual reads and writes rather than just writing a number of bytes. I think Bruno's suggestion would actually make the most sense, given that the structure is packed as of some of the recent commits.

As for the member variables, we chose to change that because when writing a gain file the file header remains the same for the same camera, so it was simpler to save the header on load into a member variable, and then just write the same header to the top of the new gain file.