Volume builder

Volume Builder.
This plugin prepares previews for a number of 4D data sets. It assumes that 4D data set is represented by the directory with a number volumes. Every volume should be represented by a folder with 2D data slices. The plugin does scaling and slicing for each data set. The results of scaling and slicing of the volumes for a data set are stacked in 4D TIFF stack for each slicing direction.

Changes:
- UI for TaskList is represented by TaskListControl;
- Task validation was added;
- Progress bar was removed;
- Builder now run in parallel thread to display statuses of the tasks in real time.