Introduce "Directory Defaults" for file libraries

This allows the sysop to configure the settings to be used for newly-created and auto-added directories without requiring any "template" directory to be configured. The "template" directory concept goes away (so in this way, File libs/dirs are now different from Message groups/subs in how bulk configuration is done).

The Lib->Clone Options menu option was moved to Lib->Directory Defaults->Clone Settings and no longer uses the first sub or the template sub but rather the configured directory defaults to be cloned into all dirs in the lib.

I decided to make the dir_defaults their own sections in file.ini rather than combining with all the other lib settings (and deconflicting key names such as "sort" and "settings"). This also allowed me to use the same cfg read/write functions for those directory settings and lib's directory default settings.