Seebs/grid dev 3

Okay, this is another try at making a usable color/scale kind of grid.

Step 1: Add an optional color argument to Draw() calls.
Step 2: Implement it for a couple of likely draw types.
Step 3: Move the logic for DrawGrid() from MOAIProp into MOAIGrid.
Step 4: Create a new MOAIGrid subclass which has a slightly more powerful draw routine, and also allows specifying additional traits.

The new design uses palettes rather than inline arbitrary colors largely for space reasons; it's pretty likely that, in many cases, a palette lookup of a smallish number of colors will be adequate, and it'll save a ton of space for a large grid.

I've found a couple of minor issues (a documentation typo), and provided hooks for setting the alpha channel separately per-item as well. This gets the functionality to a point where it can do most of what I was previously doing using Corona, and do it much more efficiently, too.