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