Make clicking on the canvas toggle pause state of the game

It seems clicking outside the canvas also make effect.
Enable towers to move position by mouse dragging
Make towers save and load positions between sessions with localStorage

Now that we can move towers around by mouse dragging, we want towers'
positions get saved.
Add get state, set state and reset buttons to createjs_game.html

Those buttons are used to control game states.
Make keyboard 'P' and HTML button toggle pause state instead of click

Previously, pause state was toggled by clicking anywhere on the screen
including buttons.  It has been somewhat annoying to see the pause state
alters whenever any button is cilcked.  Now that we added a button and
shortcut key for pausing, mouse clicking is not necessarily requied.