Update doc, internal links, layout
- Internal links added between :
- Reference widget API and
- solid-display, solid-form, solid-form-search, solid-table pages.
- Internal links added between :
- concerned attributes in List attributes and
- solid-form, solid-form-search, widget-mixin, store-mixin, validation-mixin pages.
- Add validation-mixin in index.html.
- Add solid-table attributes in attributes list.
- Layout for paginate-mixin, grouper-mixin.