Merge branch 'gsoc-importers'

This commit merges my work on advanced statistic importers built on
StatSyncing framework. More user-oriented details can be found on my
blog: http://konradzemek.com/category/gsoc/

The commit also includes changes to the ChangeLog file.

FEATURES:
 * Statistics synchronization between Amarok collections and
  Amarok 1.4, Amarok 2.x, Apple iTunes, Banshee, Clementine, and
  Rhythmbox track databases.

CHANGES:
 * "Import" button under Configure Amarok -> Local Collection no longer
   serves to import statistics from Amarok 1.4 and iTunes, and has been
   renamed to "Import batch file" to reflect the change.
 * Configure Amarok -> Metadata tab includes new buttons to add and
   reconfigure synchronization targets.

REVIEW: 113272
REVIEW: 113275
REVIEW: 113277
REVIEW: 113278
GUI: Added StatSyncing provider creation and modification dialogs. Old
     importers' dialog changed to only support batch file importing.
     New buttons added to the Metadata configuration tab.
DIGEST: Amarok advanced track statistics importers GSoC project merged.
     Please see http://konradzemek.com/category/gsoc/ for more info and
     screenshots.