Finish v0.3.3
UI.popup: small fixes

made background transparent
UI.popup: added @visible instance property
UI.popup: send the shadow and borderRadius properties to the popup iframe
UI.popup: refactored part of resize into _cacheStyle
UI.popup: append now replaces the old content
UI.popup: added popup.window
UI.popup: fixed popup loading on firefox
Release v0.3.4
Finish 0.3.4