JXR: fixed read of BGR32 and RGB555 formats
The patch includes the following fixes:
- RGB555 corrected wrong type usage (was RGB565)
- BGR32 converted to RGB24 (conversion supported by JXR library)
The read test was done using ITU-T_T.834 (2014-10) Conformance Suite. As reported by the ITU website, the suite can be downloaded free of charge, but I don't think I can include them in our test cases.