Fix for USE_HOME_DIR memorial directory

The memorial directory for Cataclysm, when compiled with USE_HOME_DIR=1, would be created in the directory the user played the game in, as opposed to '~/cataclysm-dda'.

I have reworked memorial_file to not use 'string_format("memorial/%s%s.txt"' (the culprit), and instead changed it to use FILENAMES["memorialdir"]; I also made a change to how unicode is sorted out based on std::locale("C") locale. All unicode glyphs are now represented as '_', as well as spaces.

Format is still "player_name-timestamp.txt"

-Davek