Add Qml component “Frame“.

The Frame component is an ApplicationWindow with its own title bar. The
title bar is half transparent (25%) and provides a minimize, a maximize
and a close button. The “toolBar“ has been overwritten and sets the
component to show in the right angle of the title bar. The Frame is
movable (own implementation) and resizable (window manager).

The Collection does not provide it search field anymore. To search the
current model, use following code:

    collection.model.search = new RegExp(text, "i")

The CollectionMenu component has been removed. Will be mocked-up and
refactored in future versions. Basically, we want a ListView component
which queries the local database based on each item's “query“ property.

The SearchFieldStyle user-interface component has been modified to be
displayed in the Frame's title bar.
Merge branch 'ui-mockup'.
Add support for sections in CollectionView.

The Collection component activate sections in the CollectionView if an
artist is selected. When sections are activated, an album section is
shown in front of it's containing songs. In this mode, the delegate only
displays the song title and skips artist and album properties. To work
like that, we had to use a Loader component and move the delegate Qml
code into it's own file (missing context).

The LastFMProvider makes the “rounded“ feature optional. To make round
pictures, use image://lastfm/ARTIST/ALBUM?rounded. Otherwise the picture
is draw in a normal rectangle. Instead of scaling down pictures to the
requested size, we let the Image element scales the full picture.