Removing unused files. Thanks @gvwilson, it looks good.

Merging CSS from styles repository

Merge branch 'update-template-no-css' of github.com:fmichonneau/lesson-template into update-template-no-css

add missing bracket

Upgrade bootstrap

Conflicts:
	css/swc-bootstrap.css
	css/swc.css

add new line after list

this PR replaces #145 which also included the changes to the CSS.

otherwise, during the html conversion the ul and li tags are not placed where
they need to go.

Join CSS from site and lessons

As per swcarpentry/lesson-template#140, but only the core CSS
changes.

-   Remove extra space before title of boxes
-   Remove background color of boxes when printing
-   Add "Input", "Output" and "Error" tips for code blocks
    when printing
-   Avoid duplicate lines

and "learning objectives" box.

As per swcarpentry/lesson-template#140, but only the core CSS
changes.

Improve script to setup labels

Validator should check that required files exist

Use unified CSS from site.