Initial commit for oFono extension

oFono extension will be used to enable/disable modems,
enter pin and monitor modem status via ofonod.
The extension will be supported on gnome-shell ver 3.4+.
Create Basic extension
Enumerate Modems via manager API
Add a Status area to indicate modem status
Add "Disabled", "Enabled" and "Online" states to the status
Track SimManager interface

Use the "Present" and "PinRequired" properties of the SimManager
Interface to update the status.
Use the dialog-password Icon to indicate that SIM PIN is required
Track SIM PIN retries property
Add a PIN dialog

Add a dialog to enter PIN/PUK.
Add Retry count for SIM PIN dialog
Add PUK/PUK2 specific dialog

Use ResetPin to enter PUK/PUK2.
Add a label for no modems

When no modems are detected a "No Modems detected" label is displayed.
Extend extension icon to use the edge, 3g icons

Using the bearer property of ConnectionManager interface
we can determine the bearer technology. We update the icon
accordingly.
Treat umts bearer as 3G

when the bearer is umts, set the icon to 3G.
Use Attached property instead of Online

Modem's Online property does not signify online status.
It only indicates radio state. We rely on Attached property
for availability for GPRS.

Using "Available" instead of "Online" for status as the later
is confusing in this context.
Use enums for status
Use a iterating function to select extension icon
Remove a status debug message
Check for APN

If there is a context with type internet without a APN
prompt the user to enter an APN via a dialog.
Do not Add test modems to the extension