Force UTF-8 encoding for config files

Use UTF-8 for all config file reading and writing, with both files and resources.

Fixes an issue with weird characters showing up in chat formatting. Bukkit was simply using the local default encoding for config file I/O, so if, for example, you compiled a plugin on Linux/OSX and then ran it on Windows, the YAML files in the jar would be UTF-8 but would be read as ISO-8559-1 and chars above 127 would get mangled.

Any existing config files that are not UTF-8 encoded will have to be converted, though if they only contain strings from the default config, they are probably already correct when read as UTF-8.

Also, any plugins used with SportBukkit must have config file resources encoded as UTF-8, which should be the case if they are compiled on most non-Windows platforms.