Upgrade to Bootstrap 3 (and more)

Demo here: http://dev.jerivas.com (Please help me fix the weird caching error at /shop).

These changes upgrade Cartridge to Bootstrap 3. Aside from the regular changes regarding CSS classes, I've tweaked the following:

- Cartridge in general behaves better in small devices. The category, product, cart, wishlist, and checkout templates are much more responsive.
- Use the same indentation and comment styles in cartridge.css as the Mezzanine CSS files.
- Replace {{ STATIC_URL }} with the {% static %} tag.
- Use Mezzanine's Magnific Popup as product image viewer. Now we get product galleries for free!
- All indentation was converted to spaces.
- Products displayed as a grid now have the same height and should not cause layout issues.
- The stylesheet (cartridge.css) is smaller. This might not be immediately obvious because it now uses the "one rule per line" syntax, but there are fewer rules and selectors. 

I've also discovered some bugs and areas that may need tweaking in Mezzanine and Cartridge:

- When I upgraded Mezzanine to BS3, I also made non-field errors appear as part of the form rendering tag (fields_for). A problem arises in Cartridge where multiple form errors appear, one for each fieldset. I'll rollback the changes in Mezzanine and this should be fixed.
- The "Order history" button is currently being shoe-horned into the account_form.html template. We should add a {% block %} in Mezzanine and extend it in Cartridge.

I'll get these changes into Mezzanine in the coming week. Please checkout the demo and leave your feedback.