Core: added Modernizr.details test and load polyfill
Expand/collapse all: initial v4.0 commit of plugin

1. User can now specify their own expand/collapse all link element.
2. Type of link element is set with [data-type] attribute.
3. Link elements can be restricted to only expanding/collapsing
details within a given parent using [data-parent] attribute.
Merge pull request #2943 from patheard/expand-collapse-all

Expand/collapse all: initial v4.0 commit of plugin