javascript block

![screen shot 2014-04-27 at 6 35 30 pm](https://cloud.githubusercontent.com/assets/597897/2812483/ae34ef4a-ce5c-11e3-9271-2515023c623f.png)
![screen shot 2014-04-27 at 6 26 53 pm](https://cloud.githubusercontent.com/assets/597897/2812484/b0ce723a-ce5c-11e3-8bd0-311b0e779260.png)

adds support for javascript modification of messages. streamtools: now with array modification!