Explicitly disable browser native spell check in send pane

![screen shot 2014-09-26 at 11 08 29 am](https://cloud.githubusercontent.com/assets/5728307/4425367/00401882-45a9-11e4-8d57-fa6b14f998ca.png)

Sometimes, spellcheck shows up in the `SEND TO` section of the send pane. This can be confusing to some users since an address can be valid but there is a red line showing underneath signifying something was wrong.

This PR uses the new HTML5 spellcheck attribute. Read more about it's history and compatibility here: https://blog.whatwg.org/the-road-to-html-5-spellchecking