WebDAV file sync overhaul for 5.0

Also:

- Remove last-sync-time mechanism for both WebDAV and ZFS, since it can
  be determined by storage properties (mtime/md5) in data sync
- Add option to include synced storage properties in item toJSON()
  instead of local file properties
- Set "Fake-Server-Match" header in setHTTPResponse() test support
  function, which can be used for request count assertions -- see
  resetRequestCount() and assertRequestCount() in webdavTest.js
- Allow string (e.g., 'to_download') instead of constant in
  Zotero.Sync.Data.Local.setSyncState()
- Misc storage tweaks

resource/schema/userdata.sql

@@ -1,4 +1,4 @@
--- 80
+-- 81
 
 -- Copyright (c) 2009 Center for History and New Media
 --                    George Mason University, Fairfax, Virginia, USA
@@ -261,8 +261,8 @@ CREATE TABLE libraries (
     editable INT NOT NULL,
     filesEditable INT NOT NULL,
     version INT NOT NULL DEFAULT 0,
-    lastSync INT NOT NULL DEFAULT 0,
-    lastStorageSync INT NOT NULL DEFAULT 0
+    storageVersion INT NOT NULL DEFAULT 0,
+    lastSync INT NOT NULL DEFAULT 0
 );
 
 CREATE TABLE users (