Add start/end screen and countdown timer

Note: Press ESC to end the game early.
Merge branch 'gh-pages' of https://github.com/dobesv/1gam-Druid into gh-pages

Conflicts:
	images-for-spritesheet/base-tree.png
	images-for-spritesheet/spritesheet.tps
	images/spritesheet.png
	js/spritesheet.js
Tweak the home tree position.