Extract annotation fixtures into a separate module

Also make all of the fixtures pure functions and move
the logic for setting up the drafts fake into the
createDirective() function in the annotation tests.

h/static/scripts/test/annotation-fixtures.js

+/**
+ * Return a fake annotation with the basic properties filled in.
+ */
+function defaultAnnotation() {
+  return {
+    id: 'deadbeef',
+    document: {
+      title: 'A special document'
+    },
+    target: [{}],
+    uri: 'http://example.com',
+    user: 'acct:bill@localhost',
+    updated: '2015-05-10T20:18:56.613388+00:00',
+  };
+}
+
+/** Return an annotation domain model object for a new annotation
+ * (newly-created client-side, not yet saved to the server).
+ */
+function newAnnotation() {
+  return {
+    id: undefined,
+    $highlight: undefined,
+    target: ['foo', 'bar'],
+    references: [],
+    text: 'Annotation text',
+    tags: ['tag_1', 'tag_2']
+  };
+}
+
+/** Return an annotation domain model object for a new highlight
+ * (newly-created client-side, not yet saved to the server).
+ */
+function newHighlight() {
+  return {
+    id: undefined,
+    $highlight: true
+  };
+}
+
+/** Return an annotation domain model object for an existing annotation
+ *  received from the server.
+ */
+function oldAnnotation() {
+  return {
+    id: 'annotation_id',
+    $highlight: undefined,
+    target: ['foo', 'bar'],
+    references: [],
+    text: 'This is my annotation',
+    tags: ['tag_1', 'tag_2']
+  };
+}
+
+/** Return an annotation domain model object for an existing highlight
+ *  received from the server.
+ */
+function oldHighlight() {
+  return {
+    id: 'annotation_id',
+    $highlight: undefined,
+    target: ['foo', 'bar'],
+    references: [],
+    text: '',
+    tags: []
+  };
+}
+
+/** Return an annotation domain model object for an existing page note
+ *  received from the server.
+ */
+function oldPageNote() {
+  return {
+    highlight: undefined,
+    target: [],
+    references: [],
+    text: '',
+    tags: []
+  };
+}
+
+/** Return an annotation domain model object for an existing reply
+ *  received from the server.
+ */
+function oldReply() {
+  return {
+    highlight: undefined,
+    target: ['foo'],
+    references: ['parent_annotation_id'],
+    text: '',
+    tags: []
+  };
+}
+
+module.exports = {
+  defaultAnnotation: defaultAnnotation,
+  newAnnotation: newAnnotation,
+  newHighlight: newHighlight,
+  oldAnnotation: oldAnnotation,
+  oldHighlight: oldHighlight,
+  oldPageNote: oldPageNote,
+  oldReply: oldReply,
+};