netlink: initial netlink uevent monitor
utils: added var array list append and destroy
process: added ni_shellcmd_fmt_arg, cleaned up

- allow NULL as argument to ni_shellcmd_new
- added ni_shellcmd_fmt_arg formating one argument
- cleaned up reference counting functions and usage
util: Fix return state of ni_var_array_get functions

Change return code to:
 - 0  in case of object not found
 - 1  in case of object found
 - -1 in case of error

Rename ni_var_array_get_interger and ni_var_array_set_interger
to ni_var_array_get/set_uint.
Merge pull request #232 from mtomaschewski/wait-device-ready

netlink: initial uevent monitor
client: Config prio handling based on ifindexes
Merge pull request #235 from pwieczorkiewicz/ifindextoname