Support using a DB baseline for faster program startup.

Use by specifying the JVM argument

    -Dorg.simantics.db.baseline=<path to baseline zip file>

where the baseline zip file must contain two directories:
* db/ which contains the initial database version
* .metadata/.plugins/org.simantics.db.indexing which contains the
  initial database index

During baseline initialization, the specified zip file is extracted
directly at the root of the workspace directory.

The baseline file is hard-linked/copied under the workspace root as a
file called `.baseline`. If this file exists, it indicates that the
workspace has already been initialized from a baseline archive and
should not be initialized/updated anymore.

Limitations:
* Automatic ontology updates or installation of new ontology plugins is
  disabled when a database baseline is in use.

refs #7211

Change-Id: Id67156c65047b429af71e0eab83b31a5d2fd5117