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/" target="_blank">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/" target="_blank">http://konradzemek.com/category/gsoc/ for more info and
screenshots.