restapi: bookmarks

- Add support for bookmarks to the REST api.
- The following URLs/verbs are now available:
  - /ovirt-engine/api/bookmarks (GET) get a list of book marks.
  - /ovirt-engine/api/bookmarks/{id} (GET) get book mark details.
  - /ovirt-engine/api/bookmarks/{id} (PUT) update book mark.
  - /ovirt-engine/api/bookmarks/{id} (DELETE) remove book mark.
  - /ovirt-engine/api/bookmarks (POST) add new book mark
- The standard json and xml are available. The format is the following:
  <bookmark>
    <name>The name</name>
    <value>host.name=something</value>
  </bookmark>
or
  {
    "name": "The name",
    "value": "host.name=something"
  }

Change-Id: I068194732a45223dae22c18ffee5aaa0f3ec930d
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1075556
Signed-off-by: Alexander Wels <awels@redhat.com>