New <b style=color:red>beta</b> release 2.1.6

Some more internal fixes and kludges were applied.

  * The perhaps most interesting addition is support for **Drag'n'drop**

    <img width=600 height=400 alt="DND station export to Desktop">

    Now it's not likely to be used much in reality. But was an important milestone, despite the development anger it caused.
    Streamtuner2 was always meant as data source, not just a self-contained data hog. DND required a little more cleanup to the internal playlist conversion system. But now really simplifies bookmarking radios to preferred audio players or playlist managers.

  * The configuration dialog got a little overhaul for clearness. Channel and feature plugins are now in separate tabs.

  * Some more Gtk3 workarounds were applied.

  * The UbuntuUsers plugin is now bundled per default.

  * Temporary files don't pollute `/tmp` anymore. Instead there's now a subdirectory created on startup. And `reuse_m3u` is actually honored now.

  * Jamendo `feeds` are now supported, and the JAMJSON playlist type internally converted. Thus the deprecated v2 API isn't used any longer.

  * As further workaround for Python3 on Gtk3 there's now a no-threading mode or `--nt` cmdline option.

  * Some bugfixes in the search module, browser/homepage starts, more catious partial stream refreshing, application state restoration and initial startups.