Use updated minizip version for unzip

The implementation is now in framework/minizip/*
instead of framework/Unzip.cpp

This was version 0.15beta, now we use 1.1 from
zlib 1.2.7/contrib/minizip

Some code had to be adjusted for this, but it got
cleaner on the way
Replace custom unzip functions with standard ones

unz[SG]etCurrentFileInfoPosition() isn't needed anymore,
because newer minizip versions have unz[SG]etOffset() for
that purpose.