Export schematic

Diagram export to images was extended to entire schematic. Now not only diagrams can be exported to raster or vector images. By clicking on "Export as image" item in File menu you can export entire current schematic or display page to PNG, JPG or SVG format. By right click menu in diagrams you can export diagram only. It's able to export only selcted area of schematic. Resulting image can be monochrome or coloured. 
![export-to-graphics-dlg-new](https://f.cloud.github.com/assets/4920080/1795698/2f8d5838-6a31-11e3-923f-0a28dac26e99.png)

![export](https://f.cloud.github.com/assets/4920080/1795700/515c0108-6a31-11e3-920b-46db628c4df5.png)



 Also this pull request contains bugfix for qucs-library. Component description in right area of window updates only by clicking on component in component list. If you select component by pressing Up and Down keys on keyboard component descroption not updates. Now component description updates if selected component is changed in result of any action, including pressing Up and Down keys on keyboard.