Merge pull request #6726 from visiblelight/screenshot

Add a new utility function to snap the screen
add const to ui framework methods
add const to UILayout
add constness to UIListView
add constness to UILoadingBar
add constness to UIPageView
add constness to UIScrollView
add constness to UISlider
add constness to UIText
add constness to UITextField
add constness to UIButton
add constness to UICheckBox
add constness to UIImageView
add constness to UIVideoPlayer
add constness to UIPageView's removeAllPages method
Merge pull request #6903 from andyque/addConstness

add constness to ui framework