Android - Change SDK version to work with QT 5.10

Summary:
The latest KPhotoAlbum does not work with the Androis app in Google Play.
To make it compile with QT 5.10, the minimum Android SDK supported has bumped to 16.

Reviewers: KPhotoAlbum, johanneszarl

Reviewed By: KPhotoAlbum, johanneszarl

Subscribers: johanneszarl

Tags: KPhotoAlbum, Android

Differential Revision: https://phabricator.kde.org/D10138