Display modal window for preview of the imported data

![inspire - high-energy physics literature database](https://cloud.githubusercontent.com/assets/3083746/4151698/5230e31e-3448-11e4-8894-a7e4885fb1dd.png)
![inspire - high-energy physics literature database 1](https://cloud.githubusercontent.com/assets/3083746/4151697/522d8368-3448-11e4-8fe4-b3efce92d47c.png)
Document all the functions with parameters. I've used this tool http://yui.github.io/yuidoc/ but you can try out sphinx which we use for python if you want. If you try sphinx try to compile the documentation to see if it really works with js.

Add default options as `PreviewModal.defaults` with empty `ignoredFields` and empty `labels`. Document them there, and add a line to merge `options` with defaults in the constructor. You can look at conferences typeahead as an example.