consolidate `.alert-block` styles into `.alert`. shift placement of justified CSS for nav component

BS3 commits d0b94ead9a660adeca599b2cc49ce5134d432f2f,
048e19b8921ff0cae8ade7ace7700f0563c1fb82
JS: update to latest BS3 build
consolidate `.alert-block` styles into `.alert`

BS3 commit d0b94ead9a660adeca599b2cc49ce5134d432f2f
Added short instruction for obtaining respond.js in example HTML code (see description).

BS3 commit 21be3efad3b1392ebc15acf082cbf3ae83437420
Removed data-toggle class when it wasn't been applied

BS3 commit 646700957242024828b859cc0bfacbfa0c20ac9c