add dev dependencies to package.json
Setting up test environment (Karma + Mocha) for Leaflet.Draw.
	-added Leaflet and testing dependencies to package.json
	-added spec folder + test libraries
	-added 'test' task to build.js and package.json
	-added karma config file (spec/karma.conf.js) and some miscellaneous spec helpers (leaflet-draw-include.js, leaflet-include.js, leaflet-deps.js)