fix 10767; current .img-thumbnail is equivalent to old .img-polaroid

BS3 commits: 29935e4e26df6768e8bd710dbd33a3c5fb757153
deprecate .hide; fixes 10446

BS3 commits: c4e7e3c933db27bf82b4190ed9c522bd1850c82f
avoid using the term "assets" due to potential confusion

BS3 commits: f503efc49086becc312665000fcbce4b9df3750d
move /assets/ to /docs-assets/ ; fixes 10715

BS3 commits: 8aa5181126d9480eef502403aa98e469a3597826
run grunt dist

BS3 commits: b80f58b336cd7a4b59d704ff4c311cbf8edf5e51