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.