Selection based sharing

Loads of cross-browser issues, so this is only active on non-touch devices.

![screen shot 2014-10-31 at 16 10 12](https://cloud.githubusercontent.com/assets/4549425/4863951/848d05fc-6118-11e4-9d79-e36aa18836e7.png)

Yep, good idea. I've got to add another option to the buttons, so I'll do this then.