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)

those are all good points, and I guess it boils down to a matter of personal taste.

I understand about the analogy with ```stamp```, but I also like how you move the sprite to the "end" of the stamped text, like a typewriter. But this (I think excellent!) behavior contradicts the "stamping" metaphor. Therefore I'd suggest a "draw text" metaphor. The benefit of *not* actually drawing the text unless the pen is down but *still* moving the sprite accordingly is that it lets users write exciting applications, such as even text editors, themselves, in which they can also delete parts of a stamped text again, or change its color.

I like pixels, because they correspond to the line size. If you draw a line with a pen size of 12 it will be the exact same height as a drawn text of the same size, and you can use that to "overdraw" something (or to delete parts of the text). Of course, this requires you to adjust the position of the sprite before drawing the line, as well, because lines are drawn centered, but at least with 'px' this is achievable easily.

Yes, the default pen size is 1, and the default is for the pen state to be "up". This could be a problem when users first start exploring what the block does. But most browsers have a minimum font size at something around 6 px anyway, so it's very likely users will see *something* and even be able to read it, they just can't make it any smaller than their browser settings let them (which happens to be the same for 'pt' anyway).