Label block

This replaces #362  and makes the text block a very simple label text block. 

It takes in a string, and a font size (in point values). 

It will:
* Rotate text with the sprite
* Move text to the end of the word
* Draws text at alphabetic baseline
* Always stamp LTR. There will need to be a bit of work done for RTL.

Example:
![screen shot 2014-06-29 at 10 22 34 am](https://cloud.githubusercontent.com/assets/1505907/3423921/a02170cc-ffb2-11e3-9d27-0bd111a033d5.png)

Well, @brianharvey also discussed this, but the relation between pen size and font size isn't very clear at all. The default pen size is 1, but that doesn't mean the point or px size should be 1. If I make the pen 2 or 10, what happens? I don't think the connection is clear.

The reason I had the text be drawn is because I was thinking of this block as somewhat analogous to the `stamp` block, where `stamp` stamps regardless of pen state. The current behavior also allows you to easily underline text if you'd like. I can see the benefit of doing it your way as well (and if the text stamping is connected to the pen, I agree about not drawing a line). Hmm. How does Logo traditionally do it?

I have no real attachment to the name at all, Brain suggested that `label` was a good term from logo. Draw text is also clear.