cleanup of core/types

See merge request !1

switch to unit-system

See merge request bahn-simulator/libtrainsim!1

 this makes it easier to keep track of all the
 properties that may be used. It also allows for
 all of the addition to happen in one place.

  This commit cleans core/type up.
  libtrainsim::core::clamp is replaced by std::clamp
  libtrainsim::core::version now uses a tuple to store the data.
  This makes comparing two versions easier and cleans.
  The new compare operators are also tested in the unit tests.

This reverts commit 0432b62b

adding conditions to backend.cpp which should not be needed since they are only compiled if there is support but windows has some problems