HP overlay, keyboard shortcuts, restart button and axis numbering in render

* Adds an HP overlay showing the remaining hit-points of each bot.
* Adds keyboard shortcuts to skip forward, back and toggle pause (right, left and space respectively).
* Adds a restart button.
* Adds numbering down each axis to enable easy grid coordinate location.
* Deletes canvas objects to fix the slow down and delay closing the render.
* Starts the render automatically as better default and because of the ease of restart.