Standard location for `res` & `cache` directories

[Benoit Favre]

Currently, the jtrans stores resources in the directory where it is run and asks for downloading them if run from a different directory.

It would be great if a global location was used to store resources. It could be the directory of the jar file (http://stackoverflow.com/questions/320542/how-to-get-the-path-of-a-running-jar-file), or a specific location passed as a command line argument.

[Iliyas Jorio]

Also applies to cache