Conversions: Editable fields

fixes #745  (eventually).
@chrismorast i need some design pointers for this one, SS below
![input](https://cloud.githubusercontent.com/assets/1424236/5159116/a5b1172c-737a-11e4-8f4e-9fd65c16335d.png)
.ddgsi-chev-down isnt working as expected? Went with the flat buttons, they seemed to suit better than those in the styleguide, what do you think how we should update this (color changes etc)? 
Btw, I was of the opinion that we could replicate this with currency etc, so we could use this over there as well.

//cc @moollaza @mwmiller 
@mintsoft  guys could you list me the explicit cases we should cater for this one? (like temperature, rounding digits etc)

P.s. Dont mind the mess, ill clean up when we finalize the design :smile: