REFORM-1016 REFORM-1132 Add flexibility to perform checksum comparisons at the end of a test (#57)

* Move PathLink from TestReport.cc -> Paths/PathLink.hh

* Move TestFilesystem.hh -> Paths/Filesystem.hh

* Add macros (particularly BASE_TEST()) in TestCase.hh to create a
  wrapper for the Catch2 macro TEST_CASE() (or any other test macro
  that defines a void function) to allow checksum comparisons to be
  performed at the end of a test.

* Remove timing information and empty lines from checksum
  reports. Consequently, remove filter_report() from TestReport.cc and
  replace it with a simple copy.