refactored usage of DomHelper in one more place
refactored Widget::replacePlaceholders() a little using Future(Promise)
Future(promise) improvements:
* added when() method to link the Future completion to another Future(s)
* fixed bug when done() is called multiple times and after the Future's completion
CSS-files onload-waiting feature:
* css/browserManager::load() is now returns a Future which completes when the file is loaded to browser. Cross-browser implementation and feature detection is inside.
* added special future to the Widget class (not instance) _cssPromise, which is completed when all css-files for that widget class is loaded
* added another special future to the Widget instance (_widgetReadyPromise), which is completed when all css-files loaded and all behaviours are initialized for the widget and all it's children
* Widget now have new public method ready() which returns that promise.
added completed() method for Future mostly for debugging and temporary hacking purposes
in normal state there shouldn't be necessity in such method
* used new widget's fully ready feature in dynamically re-rendering and creating new child widget
* temporary patched bug caused by redundant calling of browserInit() for some widgets when browser-side page switching process applies