Topic/unit conversion prompt

This is a basic working version. The importer section looks like this:
![screenshot from 2014-12-09 16 16 39](https://cloud.githubusercontent.com/assets/1699455/5366050/c6de5572-7fbe-11e4-8885-42029594cdb2.png)
And then when you select a file, it becomes this:
![screenshot from 2014-12-09 16 15 50](https://cloud.githubusercontent.com/assets/1699455/5366035/aa88b764-7fbe-11e4-9367-658810d2f43e.png)
And it clears after you click submit.

Input welcome.