Do not enable wifi

For some reason, this do not works on all devices. Sometime wifi is switched on and never
switch back off.
A inventory software should not "mess" with the network interfaces, if wifi is off this address
should not be reported.
use variable name and not magic number
change adress detection

We use WifiManager first, it give us lot of info and is easy to use.
Then we use lowlevel java.net.NetworkInterface to get all the other ip
(3g/ethernet/...)
use OCSSettings instead of direct call to PreferenceManager
change inventory file name (host + date)
fix unit conversion bug for cache

dureeCache is in millisecond, so must be d
remove OCSFiles singleton

We cannot have a reliable timestamp as filename with a singleton.
Moreover, constructor was public and the call to initInstance is confusing.
Create a new file (with a new timestamp), each time we want to write.
force inventory with OCSEventReceiver
add extra to OCSEventReceiver to save inventory on disk

am broadcast --ez save_inventory true org.ocsinventory.android.agent/.OCSEventReceiver