Code is mainly just copy/pasted from kernel/util/xex2.cc, I've tried fixing it up to work better in a class, but there's probably some things I missed.
Also includes some minor improvements to the XEX loader, like being able to try both XEX keys (retail/devkit) automatically, and some fixes to how the base address is determined.
(Previously there was code that would get base address from optional header, code that'd get it from xex_security_info, code that'd use a stored base address value...
Now everything reads it from a single stored value instead, which is set either from the xex_security_info, or if it exists from the optional header instead.
Maybe this can help improve compatibility with any weird XEX's that don't have a base address optional header?)
Compressed XEX loader also has some extra checks to make sure the compressed data hash matches what's expected.
Might increase loading times by a fraction, but could save reports from people unknowingly using corrupt XEXs.
(still no checks for non-compressed data though, maybe need to compare data with xex_security_info->ImageHash?)
