SVGHMI: add support for "enable expressions" with arbitrary variable name assignment.

HMI tree paths can be prefixed with a variable name "@name=/MY/HMI/VAR"
Widget declarations can end with a "#" followed by a JS expression that refers to name given to variables.
Widget is disabled if expression's result is false.

Commit includes some more-or-less related generated code refactoring, that should simplify extending widget's variables attributes.

# those files are used in runtime
# licensed according to LGPL, see COPYING.runtime 

images/icostop24.png
images/icoplay24.png
images/brz.png
util/__init__.py
util/paths.py
runtime/WampClient.py
runtime/PLCObject.py
runtime/NevowServer.py
runtime/webinterface.js
runtime/webinterface.css
runtime/__init__.py
runtime/ServicePublisher.py
runtime/typemapping.py 
runtime/loglevels.py 
Beremiz_service.py
version.py