store auth.db and craft.db in better location

[guoyunhe]

Currently, the auth.db and craft.db is stored directly under users home directory. In GNU/Linux, the standard application data directory is ~/.local/share/Craft. So the users' home directory will not be polluted by all kinds of app data.

[OvermindDL1]

It shouldn't be in /.local/share/Craft either as that can and will fail in certain situations, it should follow the XDG Directory Specification if it wants to work on everything.