client: Add missing header file boilerplate
client: Add parameter to specify D-Bus service for method call
client: Add VPN connection helper function

Add helper function for printing VPN connections. Show also configuration
and failure states using 'C' and 'F' as configuration might take some
time and failure conveys practical information to the user.
client: Add support for displaying VPN connections

Show a list of VPN connections known to the VPN daemon.

Also allow D-Bus path names to start with numbers, as it is fine with
the D-Bus library to define such path names. Fix up help command
pretty-printing as the VPN command is slightly longer.
client: Add VPN monitoring support

When adding VPN monitoring capabilities, also clean up the monitor code.
client: Pretty-print D-Bus signed integers

To keep it more logical, rename the unsigned variable in the code.
client: Read D-Bus string type only if argument is 'Type'

A basic type was always read independent of the argument type which
on some systems lead to a crash and on others only to a warning
printout.
client: Avoid printing extra prompt on RequestInput
service: Initialize tech_data

tech_data is allocated on the stack and is therefore not initilized
with NULL.
session: Use service iterator instead of match/creation callbacks

When a new session is created we need to get the initial list
of services which match the session AllowedBearers criteria. As soon
the session is running add or removed services are tracked via the
notifier interface.

We concluded that exposing all the services is not really necessary
and therefore we are using currently two callbacks to get the initial
list. That exposes implementation details from session to service, that
is GSequence. We also need to expose the type 'struct service_entry'.

Instead doing so we are using an iterator and keep all the
implementation details in session.c.
session: Use GList instead of GSequence for service list

The hash table is now the owner of the service entry instead of
the service list.
service: Use GList instead of GSequence for service list

The hash table is now the owner of the service entry instead of the
service list.
TODO: Mark GSequence removal done
technology: Offlinemode could not be disabled if no technology was powered

If all the technologies were powered off, then offline mode could
not be disabled.

Fixes BMC#26018
service: Send proxy properties when connected or disconnected

Fixes BMC#26019