system: uci: Use config dir on uci_add and support add_/del_list

system: uci: Use config dir on uci_add and support add_/del_list

This commit makes three changes to the uci shell library:

* A check for UCI_CONFIG_DIR has been added to the command line when
adding anonymous sections. Without this change, adding anonymous
sections to configs not stored in /etc/config is not possible.

* Support for adding/removing items from lists were missing, so I have
added the functions uci_add_list() and uci_remove_list() to simplify
working with uci lists from scripts.

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
[added missing package version bump]
Signed-off-by: Petr Štetiar <ynezz@true.cz>