added the /search endpoint

The bookmarklet lookups existing annotation view a call like /store/search?uri=http://path/to/.
Every annotation doc has a property "uri".
The view "annotationsbyUri" indexes all annotation docs about that property.

The specs https://github.com/okfn/annotator/wiki/Storage#search describing the expected response.
Because of the standard response of the view is different to that expectation - the response
gets finally formated in the list function "search".

In the rewrite rules the new endpoint /search is included. It forwards to the list/view path.
Also the query param "uri" gets rewritten to "key".
bugfixes for DELETE and PUT (update)

The rewrite rules were missing the doc id.
added basic security

Currently only admins will be able to delete docs or change important properties.
deleting of annotations

The DELETE annotations/:id endpoint deletes annotations via the update handler.
Because there is actually no way to send the rev number of a doc as header or query param (via the annotateit.org widget / method "destroy") - the update handler simply add the param `_deleted: true`.

That was the last needed Operation to support the full CRUD circle.