Support building on win32 and some other fixes

Apart from the changes necessary to be able to build on win32 (not tested on linux) there is one more fix for missing includes in StringUtils.cpp.

As mentioned in the email right now there's a mismatch between `kodiplatform_FOO` variables as defined in `kodiplatform-config.cmake.in` and `KODIPLATFORM_FOO` as used in the CMakeLists.txt's of the pvr addons which results in build errors because cmake variables are case sensitive.