add support for sending repo URI via NFC

If you are on the Kerplapp main screen and you do the NFC bump, and touch
Kerplapp to send, the URI of Kerplapp's repo will be sent via NFC to the
other side.

Because NFC callbacks must be attached to an Activity, and the relevant
Interfaces weren't added until android-14, this includes a hack to launch a
different Activity depending on the platform that the app is currently
running on.  It seems to be the only way...
fix crash when reading maxage pref

an EditTextPreference will always return a String, so getInt() causes a
ClassCastException.  The EditTextPreference for maxage needs to be
retreived as a String, then converted.  It is first converted to a Float,
in case the user has entered in a decimal, and that is then forced to an
int value.
print full stack trace of caught exceptions to aid debugging

Also, use the short name in the TAG so its easier to read which class the
error is happening in.  with getCanonicalName(), it includes the whole
package name, then you need a very wide column to read which class the
text is coming from.
KerplappRepo: close apkJar on problems to prevent leaks

Eclipse was warning me, so I added this little fix.
add IP to repo name, and timestamp to repo XML header
copy icons out of the APKs into the FDroid repo icons folder

This gets the apps icons from the APK and makes it part of the local FDroid
repo, so that when people view the apps in this repo, they will see the
nice icon :)

closes #2694
run icons copy in background AsyncTask, its optional

The user does not need to wait for the icons copy to finish in order to use
the new repo, it will work fine without the icons.  So put the icons copy
in an AsyncTask without a progress dialog so that it happens in the
background while the user can do other things.

refs #2694
make Send Test Repo menu item pop up FDroid when successful

Just a little shortcut to ease testing...