Update barcode library to fix QR-code scanning

In the latest master I can't scan QR codes anymore. I'm getting this error:
```
11-07 18:40:28.814    2733-2733/org.thoughtcrime.securesms E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: org.thoughtcrime.securesms, PID: 2733
    java.lang.IllegalArgumentException: Can only use lower 16 bits for requestCode
            at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:815)
            at org.whispersystems.textsecure.zxing.integration.IntentIntegrator.initiateScan(IntentIntegrator.java:179)
            at org.whispersystems.textsecure.zxing.integration.IntentIntegrator.initiateScan(IntentIntegrator.java:140)
            at org.whispersystems.textsecure.zxing.integration.IntentIntegrator.initiateScan(IntentIntegrator.java:102)
            at org.thoughtcrime.securesms.KeyScanningActivity.initiateScan(KeyScanningActivity.java:102)
            at org.thoughtcrime.securesms.KeyScanningActivity.onOptionsItemSelected(KeyScanningActivity.java:75)
            at org.thoughtcrime.securesms.ViewLocalIdentityActivity.onOptionsItemSelected(ViewLocalIdentityActivity.java:56)
            at android.app.Activity.onMenuItemSelected(Activity.java:2600)
            at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:350)
            at android.support.v7.app.ActionBarActivity.onMenuItemSelected(ActionBarActivity.java:155)
            at android.support.v7.app.ActionBarActivityDelegate$1.onMenuItemSelected(ActionBarActivityDelegate.java:74)
            at android.support.v7.app.ActionBarActivityDelegateBase.onMenuItemSelected(ActionBarActivityDelegateBase.java:551)
            at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:802)
            at android.support.v7.internal.view.menu.SubMenuBuilder.dispatchMenuItemSelected(SubMenuBuilder.java:84)
            at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
            at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:949)
            at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:939)
            at android.support.v7.internal.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:180)
            at android.widget.AdapterView.performItemClick(AdapterView.java:298)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1113)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:2911)
            at android.widget.AbsListView$3.run(AbsListView.java:3645)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5146)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
            at dalvik.system.NativeStart.main(Native Method)
```
I guess it's because of our dependency changes and this old bug in the barcode library:
https://code.google.com/p/zxing/issues/detail?id=958

I removed the old library from the source and added the latest version via maven in the gradle build script. I also had to adapt the KeyScanningActivity to the latest version.

I only tested it on my android 4.4 device, can someone test it on a real 2.3 device?

//FREEBIE