Moved notify methods from WidgetLookup to Handler. Fixes #529
Improved logging in WidgetLookup. Fixes #530
TimePerid is used for sleep interval instead of constant number (fixes #525)
ProgressBarHandler created. Fixes #401

ProgressBarHandler was created and methods requiring sync/async
execution in UI thread were transfered there from AbstractProgressBar
class and its children.
Also as part of this commit, wrong comment in TextHandler was fixed.
Added method getItems() to interface Combo and to class AbstractCombo #532