Tweaks to WebDAV preferences
Merge pull request #235 from aurimasv/webdav

Tweaks to WebDAV preferences
Fall back to link attachments for opening item
Tweak patch from 41de387 to keep file style consistent
Pass responseCharset to subsequent doGet calls
Delete hidden browser even if processDocuments exception handler does not fail.
Merge pull request #229 from aurimasv/args

Add a way for translators to pass arguments to callbacks for HTTP requests
Fix and change extraData for item change notifications

- Some item changes were putting data in the wrong form into extraData,
  which was keeping it from being passed through in notifications.
- For item modifications, set a 'changed' object, keyed by itemID, with
  just the fields that changed as keys and their old values. For
  deletes, keep the 'old' object for now, since sync relies on it.
- Remove item.serialize() for all item changes except deletions, which
  should speed up writes (and which will leave extraData empty for some
  changes).
- Currently only item fields, creators, related items ('related'), and
  'parentItem' are added to 'changed'.

Closes #220