mapping: define NOMINMAX to prevent breakage for foo::max()

sys_clock::time_point::max() is now used and without NOMINMAX, max
is defined as a macro in a common Windows header.

This commit defines NOMINMAX in the CMakeLists.txt and removes some
commented code in mapping.cpp.

Gitlab: #41
Change-Id: I98654cbafd362417d61734c4389b11ed68ff8dd8