tools/viewer: Add status bar showing status of mouse grab
tools/viewer: Add status bar showing status of mouse grab

- Show a status bar in non-fullscreen mode

- When the mouse is grabbed, display a message explaining how to release
the grab

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr