filed: Create all files with RW group permissions
peers: Adjust umask for all peers

Adjust umask for all peers to S_IWOTH, to ensure that every file can have RW
permissions for the group.
archipelago: Use configured group

Adjust umask and group id when loading configuration. This way, each invokation
of an Archipelago or vlmc command will be executed with the proper group and
each file created, will be created with the proper permissions.