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

Again there were crucial internal changes that led to 2.1.6.

 * The "action" module has been almost completely rewritten.

     - Now can convert between different playlist formats (PLS, M3U, XSPF, SMIL, ASX, JSPF, etc.)
     - Which is used by the `%m3u` etc placeholder syntax and audio player activation. (In particular to convert XSPF down to older formats understood by all players.)
     - And this simplifies the exporting capability of the recently introduced "exportcat" plugin.

 * New tiny channels for and the UbuntuUsers Wiki radio list were added.

 * Some UI fixes help with the configuration, and keep the association of last active tabs and categories in order.

 * Specialized build for the PYZ-Package. Now using preprocess.py in the packaging step.

## bug fixes

 * The bookmarks hook was broken (missing main window reference). Fixed now.
 * And there was a few NoneType error for the cache search (happened on channels with absent "genre").