fff-hoods: Introduce sector files for custom settings

While the hood file is only set by the keyexchange/hood, this
introduces a local additional configuration in a second file.
This file is retrieved from the first configap we got in w2sta
mode, of which we save the fdff address to identify it later.
Thus, a router always "knows" its specific uplink, as long as
the gateway connection is stable; otherwise: reset.

The implementation is similar to the hoodfiles with a tmp
version and a copy in the /www/public. On the "section head",
the initial configuration is located in /etc/sectorfile and
distributed from there to other nodes. Syntax should be like
the node file, except that it only contains the values to be
overwritten.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Christian Dresel <fff@chrisi01.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>