rm pngs

not needed

user_guide_2.png default :
![user_guide_2](https://cloud.githubusercontent.com/assets/812995/2823235/c01f56a8-cf1c-11e3-9f3f-429dbd7a87de.png)

show_all_albums.png
show_all_camera_media.png
have been removed

widget_folder have been updated :
![widget_folder](https://cloud.githubusercontent.com/assets/812995/2823244/e6332df6-cf1c-11e3-8ede-ec302c605975.png)
.png

empty_preview.png is not used anymore

empty_preview.png have been updated 
![flag_update](https://cloud.githubusercontent.com/assets/812995/2823266/30adc814-cf1d-11e3-806c-76d5dfb6e770.png)