Revert commit 981f862.

This reverts commit 981f8620cdde81878bc57e418297cb94960e2856.
Ignore artist filter if only 1 artist available.

The Collection component does not change the “artist“ property if only
one artist is available (switching from “All Artists“ to the artist).
Reset search when model changes.
Show loading animation on when “total“ is emited.
Add CollectionMenu component to Audiopia module.

The CollectionMenu controls which model is shown in the Collection. It
also display/hide the XMPP component on the right side of the window. To
toggle the XMPP roster, there is a new menu entry “Show Contacts“.
Add french and german translation.

At runtime, the application search for “audiopia_XX.qm“ with the current
locale (for example “audiopia_fr.qm“ on en french system). If the file
exists, Qt loads the translation and replace all qStr() instances with
their translation. Strings for translations are search in QML files and
C++ code. To add support for a new language, extend TRANSLATIONS macro.