SLING-2989 - [Tooling] integrate with vlt once available

Support different locations of the webdav servlet. For now, harcoded to
the well-known Sling and CRX locations.

git-svn-id: https://svn.apache.org/repos/asf/sling/branches/tooling-ide-vlt@1523137 13f79535-47bb-0310-9956-ffa450edef68