fix #26: updated bundled deck.js, including the fix on browsercast

this bundle is used also for browsecast-less presentations
and thus browsercast should not unbind the space in this case
and that's solved now

consolidate badge classes to swc.css

Figures should be centered
and not overflow the screen.

the class removed are unused as we take advantage of classes provided by
Bootstrap instead.

Add documentation about card class

Better style for challenges

Fix background for lessons

There's a note in
https://github.com/swcarpentry/lesson-template/pull/182
explaining why we need to fix style for panel heading.

This makes some things look nicer (e.g. adds gradients, etc).

Update CSS to go with the SWC site template update

Fix: styles for tables in SQL lessons

Now the style is matching closely `.table-bordered` from Bootstrap.
I decided to leave the header row background blank because it was too
close in color to `#F9F9F9` - our new rule for even rows in the table.

I also increased horizontal padding by 5px on both sides, because now
that we have vertical borders it was too cramped.

Additionaly I introduced borders for every cell in the table.

Previously: table cells had no padding, which caused a visual collapse
(cell content was too close to cell neighbors). Table header rows had
dark blue background and black letters.  Tables had no space between
them and following paragraphs.

Changes:
* added 5px padding to cell contents
* changed header row background to gray-ish (I considered switching text
  color to white, but it didn't look good)
* 15px margin on the bottom of the tables (similarly to bottom margin
  used by paragraph style).