Use FilteredSelectMultiple instead of custom checkbox widget

Conflicts:
	smuggler/forms.py
	smuggler/templates/smuggler/storage.html
Use fieldsets

Conflicts:
	smuggler/views.py
Updated screenshot
Formatting fix
Added a form that lists DefaultStorage root content.
DumpStorage view creates tgz file with selected files and direcories
Test dump storage behaviour
Use BytesIO for Python 3 compat
Use FilteredSelectMultiple instead of custom checkbox widget
Use fieldsets
Renamed template
Moved root urls to /smuggler/ subdir
Allow selection/exclusion of subdirs, show number of files and total size for each dir.
Added load storage form, view and urls. Refactored form templates to inherit the same base template.