Implemented tarball generation for photos

Here is a first implementation proposal for a feature that let's you archive multiple photos. You can either download all photos in the batch queue or choose to download a complete album.

You can choose between zip and tar as output format. tar has a gzip option as well.

Here is a [test openphoto instance][1] with this branch as codebase for your convenience. Feel free to use it for testing pruposes. I'll keep the VirtualHost enabled at least until the PR get's merged.

You can sign in using thee following credentials without whitespaces

d u m m y @ t e s t . d e 
d u m m y p a s s w o r d  

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This is my first time writing something in PHP so someone more experienced should probably look for beginners security flaws or accidental bad practices.

[1]:http://c5h8nnao4.dyndns.org/