Large update. Completely renewed connection/expression mechanics.

Core
* RuntimeAttribute and RuntimeModule classes instead of previous AttributeWrapper and ModuleWrapper.
  These classes should be used while working with Modules and Attributes in scripts.

* Connection and expression are evaluated on demand by RuntimeAttribute.pull/get or by RuntimeModule.ch.
  Basically, it's like pull/push mechanics here. It results in more adequate behavior which can be used in interactive tools.
  Expression is always evaluated on top of a connection.

* Consistent API across widgets and the code.
  You can use the same functions in widgets as you use in the code (like ch, module, copyJson, etc).

* Widgets API.
  Widgets can expose own API which can be used anywhere in code.
  For example, curve_evaluate, listBox_selected, etc.
  These API is used for autocompletion as well.

Widgets
* Refactor json widget, fix bugs and make it more stable.
* Widgets support self.executor for evaluating python code within a proper context (API).
* Widgets with code editor use correct autocompletion.
* comboBox eliminates duplicates.
* listBox uses roles for items and supports multiple selection. It's much more interactive now.
* radioButton refactor.
* vector widget supports a custom dimension, column count and precision.
* fix curve widget somethingChanged emits(on release button) and zero division bug.

UI
* Evaluate/Clear expression menu for attributes.
* Highly reworked widgetOnChange and updateWidget. Now it's more suitable for interactive tools.
* Update style for attributes with connection/expression.
* Fix bug in dropEvent for modules! Also it always generates unique names for modules.

Other
* Update example.xml with the latest features.
* add runStandalone.py for running RigBuilder outside of DCC with a correct stylesheet.