Do not try to send signals with no signalManager.

When widgets are run without canvas, they lack signalManager.
Fix method call.
Provide default value to avoid AttributeError.
Use different location for settings (so they do not clash with orange2).
Allow tooltips on toolButtons.
Fix a contingency indexing bug.

contingency['iris', 'iris'] worked, while contingency['iris']['iris']
failed. The second form of indexing is used in parallel coordinates
widget.
PEP8
Add category icons and colors.

If you encounter duplicate categories, invalidating widget cache should
help. This can be achieved by running canvas with --force-discovery
flag.
Include settings defined in base classes.

cls.__dict__.items() does not return inherited members, while dir(cls)
does. getattr needs default value as some members might not be
accessible yet (i.e. staticMetaObject).
Add SettingProviders.

SettingProvider is an abstraction taking care of reading and writing
settings of a class. They allow nesting of providers and late
initialization (when initialization is done before all members that will
hold the settings have been created)
SettingProvider tests.
Use setting providers in ContextHandler.
Only draw one label for combo boxes.
Raise exception, not exception info.
Copy files from orange2 with applied 2to3.
Fixed inconsistent use of tabs and spaces.
Apply consistent code formatting.
Cleanup scaling.py.
Cleanup owparallelcoordinates.py
Cleanup owparallelgraph.py