Include PSGI app to expose cluster to other servers

Using a custom router as web framework here is not yet possible.
RESTClient is now part of core

* As it is used by ha and remoteservices module.
* run-pending-ops has been moved to core as well
* RESTClient has been unit tested a little
Added empty to NodeList
Document hostName and fqdn for developers
Added localNode attribute to nodelist elements
Added several capabilities to ha.psgi daemon

* Decode JSON from body
* Added return simple scalar
Adding support to named parameters in Router

We are now copying without blush to Django URL dispatcher
Adapted to new cluster configuration interface
Bootstraping cluster is now even more nice

* Stored cluster conf in Redis
* Unit test cluster configuration method
Fix unit test name
Added Leave Cluster action

* Is this action a requirement to do in save change process?
* Plus later action to save
Include basic support to free-format Template models

To be included in Composite
Template models are now visible out of composites
Added Template model called ClusterMetadata

To show cluster metadata and Leave Cluster button
Added cluster image for ClusterMetadata Template model
Show some Cluster fields depending on bootstraped flag

Now the UI is more or less done for this
Added some devel doc

+ Set a string to an Internal exception
Menu integration done

Cluster initial configuration UI working
Give the basis for leave cluster request
Change iface now works in a single node cluster