Corrected imports of .Net stuff - if python.net interpreter is not present everything still works - but a warning message is displayed.

Package inport/export functionality corrected/improved. Export was rewriten so that it outputs Categories/widgets/Inputs/... always in the same order as well as notifies the user what it is exporting.

subgroup querying widget now returns the complement as well. added widget for constructing tables out of sets.

The only thing person has to do to add package is to add it to mothra/settings/INSTALLED_APPS.
following files are automatically added with definitions from equal naming modules from packages.
- library.py
- visualization_views.py
- interaction_views.py
- urls.py

Improved import_package functionality - now import can remove widget's outputs,inputs and options which are not beeing used.

First approach to include static_image field in the treeview and widget. It works but still needs to be rechecked/redone by the chief architect :)

Added import/export functionality for widget definitions (for models: AbstractWidget, AbstractInput, AbstractOutput, AbstractOption, Category).
Three managment functions added:
- export_package
- import_package
- renew_uids
Help included should be enough to understand each functionality.
Everithing is 'quite' thoroughly tested, however, I STRONGLY suggest database BACKUP before doing commands import_package or renew_uids. export_package should be safe.

Merge branch 'dev_latino' into dev (last merge since separate dev_latino branch will be terminated afterwards)

New dev branch to be merged with dev_latino - nothing changed based on previous version (empty line removed from library.py in order to be able to commit)