New Skin icons and styles.
Adds LoadingBar widget and test.
Removes unused DownloadFileListener.
Changes DownloadFileWorker to return the completion as result.
Now it can be cancelled in the middle of the download.
Changed WorkerExecutor to allow multiple workers
of the same class working in parallel.

Fixed a bug where the CANCEL event wouldn't get fired because the worker was removed
from the map too early when results were launched on UI thread.
Adds DownloadManager.
Adds RepoTile to SearchGallery.
Improves SearchRepoViewTest.
Improves LoadingBar height, adds DelayedRemovalArray to WorkerExecutor and fixes CopyEntityResources worker.
Merge pull request #911 from RotaruDan/downloadableTile

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