Updated shadow values from Material Design PSD

Current values in paper-shadow do not match wiht shadows found in the PSD file: http://material-design.storage.googleapis.com/publish/v_2/material_ext_publish/0Bx4BSt6jniD7MGtzS0lpeFZUYmc/stickersheet_general.psd

I managed to get a good enough approach for z-1 using only 1 shadow, which will probably improve performance in most paper components, as z-1 is the most common value.
 
I did not found any reference in the PSD to z-3 and z-5 so I interpolated the values :)