Improve use of typing throughout Plottable, particularly the utils [use-d3-map-instead-of-object-in-new-style-plot]

- createFilledArray uses generic typing
- uniq uses generic typing and uniqNumbers is removed

Conflicts:
	plottable.d.ts
	plottable.js
	src/utils/utils.ts
this maintains types, set coerces everything to strings