Improve PictureViewer

1. Mouse wheel to zoom in/out when ctrl key pressed
2. Mouse to drag picture
Improve PictureViewer

Scroll up/down when ctrl is not pressed
bug fix: twitter '~' encode error
Improve PictureViewer

Keep position of viewport center not changed after zoom in/out
Improve text editor

Press Ctrl+Return to send
misc
Merge branch 'dev'