Upgrade to Maven Assembly plugin 3.1.0

** Bug
    * [MASSEMBLY-643] - descriptorSourceDirectory: parameter isn't used
    * [MASSEMBLY-841] - Maven Assembly Plugin throws IllegalStateException when looking for project modules
    * [MASSEMBLY-842] - Incorrect entries created in MANIFEST/maven
    * [MASSEMBLY-855] - Remote repositories ignored in a multi-module project

** Dependency upgrade
    * [MASSEMBLY-854] - Upgrade to Plexus Archiver 3.5
    * [MASSEMBLY-859] - Upgrade to Plexus IO 3.0.0
    * [MASSEMBLY-867] - Upgrade maven-archiver to 3.2.0
    * [MASSEMBLY-868] - Upgrade plexus-utils to version 3.1.0

** Improvement
    * [MASSEMBLY-711] - Add support for generating XZ compressed tarballs (.tar.xz)
    * [MASSEMBLY-858] - don't read assembly descriptor from thread classloader but plugin classloader
    * [MASSEMBLY-860] - Upgrade to Java 7