WIP: The webrunner can handle multiple Software Release at once

Let the webrunner manages several Software Releases at once. Also introduce a feature of migration between software releases for the deployed instance.

To do so, the webrunner relies more on the slapproxy, and tries to decrease the use of hardcoded data in multiple files. Also, the slapproxy's database file is not arbitrary deleted whenever the user requests slapproxy.

Now multiple Software Releases can be supplied, and opening a new one won't destroy the current instances.