Split services into separate files

Split services into separate files

The example configuration file pazpar2.cfg.dist now includes a default
service default.xml (part of etc). And default.xml includes
settings/edu.xml. The default.xml file (not to be confused with
settings/defaults.xml) is a template for jsdemo and other services.
The Debian package installs /etc/pazpar2/server.xml which is now
the main pazpar2 configuration (used to be called pazpar2.cfg).
server.xml includes services from /etc/pazpar2/services-enabled/*.xml .
The default.xml (from etc) is installed in /etc/pazpar2/services-available
and a symlink to it is created from services-enabled. The default.xml
service is unnamed and, thus, will be used by jsdemo and test1.