fix crash java.lang.NullPointerException

[taliasegev]

Our app crashed on GooglePlay automatic tests. The reason was -
Attempt to invoke virtual method 'void android.telephony.TelephonyManager.listen(android.telephony.PhoneStateListener, int)' on a null object reference

I would like to suggest a fix for the package, making it safe for use. I've added try catch, checking if object is null, and added failure callback for each function.
I've changed the version to 2.0.0 since it is a major fix, changing the functions signatures (due to the failure callback).
I believe it is important for the stability of the package, and it is much safer to use it this way.
Please approve my PR.
Example for the new use -

Telephony.getCellInfo( cellInfo => { // Do something with result }, error => { // Handle error, exception from Android native code }

Thanks,
Talia Segev

[taliasegev]

#8