Allow mobile devices and other non-drag-and-drop-enabled devices to upload files

This one has been bugging me for a while. It's impossible for touch devices such as phones and tablets to upload files to Kandan, even though it's responsive and otherwise perfectly suited for mobile devices.

I added a check to see if the current device is capable of dragging and dropping, and if it's not, it instead displays a nicely styled file upload button, which will automatically upload the file via ajax, same as the current drag-and-drop file upload.

![screen shot 2014-09-14 at 4 26 43 am](https://cloud.githubusercontent.com/assets/93607/4263464/ee3207e6-3be8-11e4-80b0-27dea790b1dc.png)