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

![robotgamegui2](https://f.cloud.github.com/assets/2941863/1578598/8be89f4a-517f-11e3-84e4-4627375e7519.png)

* 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 (by mueslo).
* 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.