DB links

Switches UI for adding layers from db's to be simple links.

![dblinks](https://cloud.githubusercontent.com/assets/83384/3224058/8a7f04f4-f02c-11e3-897d-34c7c2c7ce95.png)

Names em `data`, `data_1`, `data_2` ... etc. to start leaving it up to the user to rename them to something useful.

cc @GretaCB