Added system test for PoldiMerge

It uses the data files that already exist in the repository.
Refs #9630. Added system test for PoldiTruncateData

The test goes through three possible use cases: Too many time bins (the usual raw POLDI data), exactly correct number of bins and too few time bins.
Merge branch 'master' of https://github.com/mantidproject/systemtests into feature/9630_poldi_truncate_data_test
Refs #9436. Make test compatible with changes from #9564.
Refs #9445. Added system test for PoldiCalculateSpectrum2D

The test uses a spectrum calculated with the original analysis software.
Merge branch 'feature/9436_poldi_merge_system_test' into feature/10074_merge_poldi_system_tests
Merge branch 'feature/9445_systemtest_for_poldi_2d_spectrum' into feature/10074_merge_poldi_system_tests
Merge branch 'feature/9630_poldi_truncate_data_test' into feature/10074_merge_poldi_system_tests
Merge branch 'feature/9445_systemtest_for_poldi_2d_spectrum'
Merge branch 'feature/9630_poldi_truncate_data_test'
Merge branch 'feature/9436_poldi_merge_system_test'
Merge branch 'feature/10074_merge_poldi_system_tests'