[telephony-app] should check for network registration state before enabling the call/send sms button

[Ricardo Salveti]

Currently the telephony-app is not checking for network registration state at all, and always giving the user the possibility to do calls and send sms, even if that's not enabled by ofono.

With latest ofono (1.9phablet9), the registration property is already exported via ofono dbus api, so this just needs to be added to the app itself.

E.g.:
- NetworkRegistration.GetProperties:
root@localhost:/# dbus-send --system --print-reply --dest=org.ofono /galaxynexus_0 org.ofono.NetworkRegistration.GetProperties
method return sender=:1.15 -> dest=:1.22 reply_serial=2
   array [
      dict entry(
         string "Status"
         variant string "registered"
      )
      dict entry(
         string "Mode"
         variant string "auto"
      )
      dict entry(
         string "LocationAreaCode"
         variant uint16 50219
      )
      dict entry(
         string "CellId"
         variant uint32 12593173
      )
      dict entry(
         string "Technology"
         variant string "umts"
      )
      dict entry(
         string "MobileCountryCode"
         variant string "724"
      )
      dict entry(
         string "MobileNetworkCode"
         variant string "03"
      )
      dict entry(
         string "Name"
         variant string "TIM 3G 19"
      )
   ]

[Tony Espy (awe)]

Note, the connection manager should be able to listen for an associated PropertiesChanged signal to monitor when the registration status changes.

[Bill Filler (bfiller)]

call/send button always enabled but an error is displayed if the network is not connected