Various features/fixes (#727)

* fix(data-table): export useStaticWidth prop

* docs(data-table): add static width example

* fix(data-table): do not render table header if title/description not provided

* feat(modal): dispatch "click:button--primary" as an alias to "submit"

* test: update DataTable types test

* test(modal): update modal type tests

* docs(data-table): add clear reminder to key headers/rows

src/Modal/Modal.svelte

@@ -297,6 +297,7 @@
           disabled="{primaryButtonDisabled}"
           on:click="{() => {
             dispatch('submit');
+            dispatch('click:button--primary');
           }}"
         >
           {primaryButtonText}