[explore] refactor slice action button group (#1074)

* pull explore actions button group into component

* use button component

* make sure we render all action buttons

* test that embed code is correct

* don't need before each

* generalize modal trigger for use with plain links or icons

caravel/assets/spec/javascripts/components/CopyToClipboard_spec.jsx

@@ -0,0 +1,17 @@
+import React from 'react';
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import CopyToClipboard from '../../../javascripts/components/CopyToClipboard';
+
+describe('CopyToClipboard', () => {
+  const defaultProps = {
+    text: 'some text to copy',
+  };
+
+  it('renders', () => {
+    expect(
+      React.isValidElement(<CopyToClipboard {...defaultProps} />)
+    ).to.equal(true);
+  });
+});