Fancybox Enhancments

As promised. Fancybox galleries can be utilised by using the tag gallery instead
```
{% gallery .... %}
```
And an alternate source can be provided now to have thumbnails (G+ images makes this trivial, width + height is controllable via the url).

```
{% gallery https://lh5.googleusercontent.com/-RxG-kI3AMXA/UvtjLu7eoqI/AAAAAAAAIq0/TJ6J8gj_MCo/w1324-h1023-no/IMG_0293-edit.JPG "Dropout Repair" https://lh5.googleusercontent.com/-RxG-kI3AMXA/UvtjLu7eoqI/AAAAAAAAIq0/TJ6J8gj_MCo/w250/IMG_0293-edit.JPG %}
```

Working example here:
http://www.techman83.me/personal/2014/02/12/refit_bb.html