Emits the storageModified signal after 200 ms rather than after every single operation of Processor::addFile or Processor::removeFile

Summary:
Updates the view after 200 ms when the first database operation is performed
Since ImageStorage::commit emits ImageStorage::storageModified and rest of the model reacts to the ImageStorage::storageModified signal to update the view. this will be a better approach

Reviewers: Koko, mart

Reviewed By: Koko, mart

Differential Revision: https://phabricator.kde.org/D6896