Minimize unneeded widget redraws and blinking during redraws

[yvolk]

In Beta v.3.0.3 (on Beta testing see #320) we noticed that sometimes the widget is redrawing (and blinking) more than once e.g. on the device unlock.

We need to:

• minimize widget redraws;
• minimize or better avoid blinking (visible switching of views) during each redraw.

[yvolk]

After reading https://developer.android.com/guide/topics/appwidgets Fixed in v.3.0.4 #320