Enable privacy dropdown even when saving an annotation is disabled

 * Implement design change to allow a user to change the privacy
   setting for an annotation even if the annotation cannot
   yet be published because no tags or text have been entered.

 * Disable the hover state for the main section of the button
   when it is disabled.

T-125

h/static/scripts/directive/test/publish-annotation-btn-test.js

@@ -106,7 +106,7 @@ describe('publishAnnotationBtn', function () {
       canPost: false
     });
     var disabledBtns = element.find('button[disabled]');
-    assert.equal(disabledBtns.length, 2);
+    assert.equal(disabledBtns.length, 1);
 
     // check that buttons are enabled when posting is possible
     element.link({

h/static/styles/dropdown-menu-btn.scss

@@ -37,7 +37,7 @@
     text-align: left;
     vertical-align: middle;
 
-    &:hover {
+    &:hover:not(:disabled) {
       background-color: $hover-background-color;
     }
 

h/templates/client/dropdown_menu_btn.html

@@ -8,8 +8,7 @@
   <button
     class="dropdown-menu-btn__dropdown-arrow"
     title="{{dropdownMenuLabel}}"
-    ng-click="vm.toggleDropdown($event)"
-    ng-disabled="isDisabled">
+    ng-click="vm.toggleDropdown($event)">
     <div class="dropdown-menu-btn__dropdown-arrow-separator"></div>
     <div class="dropdown-menu-btn__dropdown-arrow-indicator">
       <div>▼</div>