[BOCA][WRITER] _write_checker has Polygon Dependency

[gnramos]

writer.BOCA._write_checker method is implemented to process if checker_file is available, but implementation is clearly dependent on Problem being created via reader.Polygon. There should be no such dependency.

[gnramos]

_write_checker function considers Problem is made in Polygon, thus using testlib.h and compiling using g++. Polygon may provide checker file in other programming languages, in which case the current implementation WILL NOT WORK. Additionally, a "checker" may exist in different formats/approaches for other e-judges, thus the current implementation would not work for such cases, effectively hampering future development for this project.