Debug build installs release dependency libraries

[ELeeScape]

In PR #820, specifically this commit, a bunch of changes were made to accommodate the special needs of cesium-unreal, including the fact that the Unreal Engine doesn't have a real debug build; even the debug build of UE links to the release CRT libs, so the debug build of cesium-unreal also links to the release CRT libs, and that cascaded back to cesium-native where as of #820 even a debug build installs the release versions of all of its dependencies (though the Cesium libs themselves are debug versions). This means you can't do a debug build of cesium-native and then link it to a typical debug build of some client other than cesium-unreal, because the CRT lib types will be all mismatched.

The result when you try (at least on Windows with MSVC) is a bunch of errors that look like this:

error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '0' doesn't match value '2'
error LNK2038: mismatch detected for 'RuntimeLibrary': value 'MD_DynamicRelease' doesn't match value 'MDd_DynamicDebug' 

The fix (I think) is that /CMakeLists.txt needs to install libs from ${PACKAGE_DIR}/debug/lib/ (here and here) if it's a debug config AND some special Unreal flag isn't set, otherwise install libs from ${PACKAGE_DIR}/lib/. I'm not sure how to best detect the Unreal condition, though, so I'll leave it to someone who know what they're doing to come up with the PR.

[lilleyse]

@ELeeScape this should be fixed in #962. I haven't tested it in Unreal though.