modal docs: ensure all <button>s have an explicit `type` attribute

BS3 commits: 1783c7072726495f9cc9b41e04d8e5180e7868a5
grunt

BS3 commits: 16f9529ed1291ed7e36b530f475b6705f9942347
grunt

BS3 commits: 5a5cf224e19f5c2e9b464d6d4b94a5f5d989d5d8
Wrap .pagination & .pager in <nav> to improve accessibility

BS3 commits: 48c67095b01406b4b8c89230bab000a4a9dd1900