implement up and down keys to navigate in the chat history, needs testing over network

don't display squares when pressing arrow keys in chat

formatting

do not hardcode CMAKE_INSTALL_PREFIX for windows, but rather put it in the script, so that custom build setups still work

Hard math to fix issue #571. Well, not really hard math, just checking if vector is in opposite direction and trait that as a special case when removing rope dividing point (this could only happens when rope sticks to land outline, so this basically fixes a bug in another bug).

oups

fix compilation with clang. fixes issue #553 - thanks to julien for reporting and to drew for the first part of the fix