Add new export / import icon for tables.

There used to be no icon for the SL-action import / export.
New:
![bildschirmfoto 2014-01-21 um 17 17 33](https://f.cloud.github.com/assets/7469/1965242/c55123b0-82b7-11e3-98f8-1bf2d80ab64a.png)

@maethu is that ok?