XCOM: add support for GOG archive, WIP

1) the midi files are missing from the GOG.com archive,
   but are well in the Steam release: why ?
   For now these are move to 'optional'.

2) roland.cat is different.
   Does it matter ?
   Is it even needed by OpenXCom ?

3) 5 others .DAT are missing.
   These aren't in universal_patch.zip either.

WARNING:game_data_packager.build:found possible "sound/roland.cat" but
it is not one of the expected versions:
    file:
/tmp/gdptmp.8q8uwc02/tmp/setup_xcom_ufo_defense_2.0.0.4.exe.d/app/SOUND/ROLAND.CAT
    size:   143866 bytes
    md5:    8421cdcbe91b1b3e4818d470f32ca859
    sha1:   14a236be4e16b7040367dea87e25549d6ff290ba
    sha256: 6d98825b620eedb563f664161f86a391d60a0102c811400382ff1d9685913836
expected:
  SOUND/ROLAND.CAT:
    size:   93853 bytes
    md5:    7194c1480e6ce2d3e188133ece4fdefb
    sha1:   None
    sha256: None

ERROR:game_data_packager.build:setup_xcom_ufo_defense_2.0.0.4.exe should have provided GEODATA/BIGLETS.DAT but did not
ERROR:game_data_packager.build:setup_xcom_ufo_defense_2.0.0.4.exe should have provided GEODATA/ENGLISH.DAT but did not
ERROR:game_data_packager.build:setup_xcom_ufo_defense_2.0.0.4.exe should have provided GEODATA/FRENCH.DAT but did not
ERROR:game_data_packager.build:setup_xcom_ufo_defense_2.0.0.4.exe should have provided GEODATA/GERMAN.DAT but did not
ERROR:game_data_packager.build:setup_xcom_ufo_defense_2.0.0.4.exe should have provided GEODATA/SMALLSET.DAT but did not