Adding Jinja2 filters for the album names: extract the date

* Thanks JP van Oosten for your help on how to use Filters in Jinja2 templates with bottle
<http://jpvanoosten.nl/blog/2013/03/24/custom-jinja2-filters-when-using-bottle/>

* Formatting dates according to Locale:
<http://stackoverflow.com/questions/985505/locale-date-formatting-in-python>
updating TODO in README: this was done in commit c31294b
New formatting filter for EXIF information f-number, exposure, …
README: Generation of all thumbnails could be done via a shell script
Simplified formatting for the focal length and f-number.