Automate encfs setup and name mount point more appropriately

Just by setting `encfs_password`, this set of tasks will:

* Create the filesystem if doesn't exist (using paranoid mode)
* Decrypted/mount it if exists but isn't mounted
* Do nothing if it's already mounted

I moved `/decrypted-mail` to exclude "mail" from its name because it's now being used for more than just mail, and I figure it was just a holdover from the "inspirational post". Better to clean this up sooner rather than later.

### Migrating an existing server ###

1. Reboot the server (or just stop the services and unmount the encfs)
2. `rm -rf /decrypted-mail`
3. `mv /encrypted-mail /encrypted`
4. Run the entire playbook to update the paths everywhere, and decrypt/mount it