Abstract and further merge filter menus

Summary:
  - Adds `PhabricatorMenuItemView` which is a non-hacky object representing a single menu item.
  - Adds `PhabricatorMenuView`, a collection of items.
  - Deletes some busted/old interfaces full of garbage nonsense.
  - Merges menu item styles from `aphront-side-nav-view-css` and `phabricator-nav-view-css`. These are old-style and new-style rules which got partially updated recently.
    - The new-style menus have a darker background (#ececec) than the old-style menus (#f7f7f7) so some of the highlight/hover colors weren't visible. I shuffled them around but something or other might need further adjustment.

Test Plan: looked at every menu I could

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1960

Differential Revision: https://secure.phabricator.com/D4036

src/applications/differential/controller/DifferentialRevisionViewController.php

@@ -979,9 +979,7 @@ final class DifferentialRevisionViewController extends DifferentialController {
     $nav->setBaseURI(new PhutilURI('/D'.$revision->getID()));
     $nav->setFlexible(true);
 
-    $nav->addFilter('top', 'D'.$revision->getID(), '#top',
-      $relative = false,
-      'phabricator-active-nav-focus');
+    $nav->addFilter('top', 'D'.$revision->getID(), '#top');
 
     $tree = new PhutilFileTree();
     foreach ($changesets as $changeset) {