Cherry-pick fixes from bugfix/10088_PartialSpectraLoading into next

Changes:

    refs #10088 Failing attempt to change loading

    (does not work correctly)
    (cherry picked from commit f17db4d62b10ac2eaee1b78b8e6c573337501bc6)

    Conflicts:

    	Code/Mantid/Framework/DataHandling/src/LoadISISNexus2.cpp

    refs #10088 Change necessary for working without precompiled headers
    (cherry picked from commit 7026fcf1ff04db4f7e8c5edd7b3dada751172bb8)

    refs #10088 Map is build seems correctly but detID-s are still wrong
    (cherry picked from commit 8cdfaf2eb7b9910235d94397ce9160a32404a734)

    refs #10088 Mainly done, checks and optimization is needed
    (cherry picked from commit 9db55ebed6bce4051ed2c393764c93339af6c168)

    refs #10088 Got rid of m_spectra_list in favor of m_specNum2SpecID map
    (cherry picked from commit 5783a2aa7e7cdc06683dcba257898ca76d35eb00)

    refs #10088 Unit tests to check the changes and correct behavior

    + final bugs fixed for LoadISISNexus2
    (cherry picked from commit c39baa82c348f4e160bcbc45d8a8610af878e2c1)

    Conflicts:

    	Code/Mantid/Framework/DataHandling/test/LoadISISNexusTest.h

    refs #10088 Doxygen errors
    (cherry picked from commit accdf340bc898d2dcd4c5842921a901bc403e966)

    refs #10088 GCC warnings
    (cherry picked from commit 032ff6f0233c00563775a5df74b6e58d4c786fac)

    refs #10088 Prospective Coverity warnings
    (cherry picked from commit b6b27700fad6ca2914395f8abaac80bbbfaf581c)

    refs #10088 a bit more tests for different options

    especially correspondence between spectra and detectors maps.
    (cherry picked from commit 86656b220058344ab822ed955fb196370111766d)