Upgrade Gradle and the Android plugin

Currently, the most mature Android Studio version is 0.8.6 beta. The beta
version requires at least version 0.12.0 of the Android plugin for Gradle,
so use that. Also upgrade to the latest supported Gradle release 1.12 in
the same run.
Merge pull request #43 from sschuberth/gradle-upgrade

Upgrade Gradle and the Android plugin
Also update the buildToolsVersion to the minimum for Android Studio 0.8.6
Add debug log output whether crash log transmission succeeded or not

Without this there is no way to tell from the logs whether the
transmission actually has happened or not. That is good to know in case of
network problems, so add some debug output.
Merge pull request #44 from sschuberth/develop

Add debug log output whether crash log transmission succeeded or not
Remove unused import.
Add CrashReporter Key to log similar to iOS.
Merge branch 'develop' of github.com:bitstadium/HockeySDK-Android into develop
Add semi-random salt to crash identifier calculation.
Change header order. Add comment that package has to come first.
Improve feedback view layout.