Fix sample app to choose proper preview/photo size that close to display size

Currently sample application uses pre-defined constant values for picture size as follows. 

> params.setPictureSize(1280, 960);

This can cause a crash when 1280x960 is not supported by a device. Instead, this PR use _getSupportedPreviewSizes_ and _getSupportedPictureSIzes_ method to obtain candidate sizes, then pick proper one. Here, proper size means that it has 1) similar aspect ratio of display and 2) similar height of display.