Pair messaging 1 953

Each screenshot kills two stones with 1 bird (I don't condone the killing of animals and therefore prefer to kill rocks instead). This is part of #953 
## No favorite pairs saved; default state (and error message)
![screen shot 2014-10-07 at 4 26 25 pm](https://cloud.githubusercontent.com/assets/5728307/4551952/b8b399b0-4e79-11e4-8f3c-eacb1658548a.png)

## Favorite pairs saved; Creating a new pair 
![screen shot 2014-10-07 at 4 27 29 pm](https://cloud.githubusercontent.com/assets/5728307/4551945/aadd3ce2-4e79-11e4-85d3-efc36713a3b7.png)

Parts 1 and 2 of https://github.com/stellar/stellar-client/issues/953
I disagree:

By having it here, we get to see the error message earlier, which IMO is a good thing.  

Additionally, formIsValid and formIsFilled are treated orthogonally in the templates:
```javascript
!formIsValid || !formIsFilled
```

If we want to have one be dependent on the others we need to clean up more than just this function.  Personally, I think it's legitimate to have isFilled and isValid be independent attributes of the form.