move file_exist to file_wrapper.h/cpp
check for io-errors when saving a character template
add checks for io-errors in various save-functions
add message if writing default mods fails
make most save methods return false if they failed to save

moved save_maps, save_artifacts, save_factions_missions_npcs to game::save

don't quit after failed saving
Merge branch 'impreove-writing-files' of https://github.com/BevapDin/Cataclysm-DDA into BevapDin-impreove-writing-files