Add live view for TX inputs. 

This is a live demonstration of how https://github.com/TauLabs/TauLabs/pull/820#issuecomment-22856941 could work. It implements a transparent slider handle representing current command control value.

![screen shot 2013-08-19 at 11 54 22 am](https://f.cloud.github.com/assets/1118185/985196/ed10d480-08b5-11e3-91e6-993cba4f46b6.png)

Colors are off, the handle doesn't look right, and it doesn't even respond to the stylesheet. However, it gives us a relative idea if this is a workable approach, or if there's too much going on on these sliders.

NOTE: There is a GCS bug that prevents one-to-one correspondence so this code doesn't show the correct channels in certain circumstances.