cleanup: reuse Bootswatch theme check
use Bootstrap 2.3.2

Note: BootstrapCDN serves 2.3.2 default as combined responsive CSS, therefore added additional checks for this. For Bootswatch themes, need to use 2.3.1 bootstrap-responsive.css
Merge branch 'bootstrap-2.3.2'
use highlight.js version 7.5. See issue #17