and use it for 'nmcli device show'.

This allows filtering output not only for whole groups, but also for individual
fields in commands that print data in groups (sections).

Example:
$ nmcli -f general.device,general.driver,ipv4,ipv6.address device show eth0
GENERAL.DEVICE:                         eth0
GENERAL.DRIVER:                         e1000e
IP4.ADDRESS[1]:                         ip = 10.0.5.228/23, gw = 10.0.5.254
IP4.ADDRESS[2]:                         ip = 5.5.5.5/32, gw = 5.5.5.1
IP4.DNS[1]:                             192.168.122.1
IP4.DNS[2]:                             8.8.8.8
IP4.DOMAIN[1]:                          mycompany.com

This will allow callers to distinguish "no such connection" from
"connection failed to activate", etc.

https://bugzilla.redhat.com/show_bug.cgi?id=1022256

Ask for confirmation in these cases:
* autoconnect=yes and connection has not been saved yet
* autoconnect=yes, but saved connection had autoconnect=no

The confirmation can be switched off with
nmcli> nmcli save-confirmation no

- show/hide status line:  nmcli> nmcli status-line yes | no
- editor prompt color:    nmcli> nmcli prompt-color <0-8>  (0 = normal/without color)

Until now we have used a static width defined for each column for tabular
output. Even if this worked in most cases, it was not optimal, because by
using too wide columns we wasted space, and in case of a too narrow column the
alignment broke. So, we need to know the longest string in a column to be able
to align columns in the tabular output. Thus, the printing has to be postponed
till we have all data available, and can find the widest column. This value is
then used for aligning while printing the data.

Arrays of NmcOutputField (rows) are inserted into output_data array. When all
data have been added, print_data() can be used to print the whole output_data
array with proper alignment.

A single row can be printed using print_required_fields().

Also, output flags are redone to better match the new output_data array.
The flags are needed for every row (in tabular output); they are stored in
the first field (NmcOutputField) for the whole row.

Addapted set_val_str() and set_val_arr() to set value type (char * x char **).
Added set_val_strc(), set_val_arrc() for const values that should not be freed.

output_data takes ownership of the data added to it and takes care of freeing
the memory.

See e.g.
https://bugzilla.gnome.org/show_bug.cgi?id=699503

It will be used to ask user for required but missing data/parameters.

glib 2.32 makes a runtime check that domain is not NULL:
GLib-WARNING **: (gerror.c:390):g_error_new_valist: runtime check failed: (domain != 0)

The command didn't delete the connection, because nmcli exited before NM could
check permissions (actually ConsoleKit didn't see the process).
Now nmcli waits for "Removed" signal or D-Bus return (error) message on "Delete"
method call.

Field values can now be string arrays. print_fields() recognizes the format and
prints values accordingly.
Setter functions was added to facilitate setting string vs. array:
set_val_str(), set_val_arr()