Multi-application support

The first commit allows to upload an archive with native libraries from an Android application. This archive is converted to debug symbols by the HockeyApp server and is used for native crashdump resolving. More information can be found here: http://support.hockeyapp.net/kb/client-integration-android-other-platforms/hockeyapp-for-android-ndk-early-access

The second commit is a quite big and complicated one, but the idea is very simple. It add a possibility to upload multiple applications to the HockeyApp server from a single Jenkins job. For instance, one may use a single job for building iOS and Android versions of an application or both paid and free versions of the same application. So this patch makes such case possible. The patch became this large because it's important to provide backward compatibility with previously saved configurations of the HockeyApp plugin.

And the third commit is just about .gitignore.
The change may cause binary compatibility issues if somebody uses the plugin in his code