Phpthumb update

Hey there,

updated phptumb usage to last available version 2.0 (https://github.com/masterexploder/PHPThumb/releases).

I added settings for:
- imagemagick_path
- quality_small
- quality_mini

This enables to have much better picture quality then with gd and 70 quality setting hardcoded.

Feel free to review and give feedback. If there are things to be fixed, let me know.


Cheers & Regards (great app!)
Mischosch