community/appstream: upgrade to 0.15.1

Libraries:

• libappstream soversion still 4, hasn't changed
• libappstream-compose soversion hasn't changed from 0, but library is not stable. Grepping for appstream-dev in aports I only found plasma-workspace, discover, gnome-software, appstream-generator and frameworkintegration. Out of those, only appstream-generator links against libappstream-compose and I am planning to upgrade to 0.8.6, which requires libappstream-compose >= 0.15.1. So upgrading should be safe.

Dependencies:

• Upstream replaced lmdb requirement with libxmlb
• Added itstool for adding translation to metainfo file
• Added missing dependencies for compose