Moved all the code related to the toolbar managment to a manager object, ToolbarManager. This object takes care of the creation of the toolbars and of the correct visualization of the selected toolbar position
Rewrote the search widget as a combination of a new widget (SearchEntry) and a controller (AlbumSearchEntryController). For that, I reacomodated some code and made a more diversified hierarchy on the widgets module, saving some code from being duplicated. Modified the code on the coverart_browser_source module to implement this new schema for the search entry. Now all the toolbar widgets from all the toolbars (topbar and sidebars) are synchronized through the controllers