Move java preferences to Ice-managed XML

[jamoore]

Suggestion from Chris: all our server configuration values could be manually managed in a single XML file which icegridnode can read and pass to all servers and which blitz can also read at startup.

This would alleviate all the problems we've had with the Java Preferences API.

[jmoore]

(In [7205]) OmeroCli: Working configuration in admin.py. See #800, #2213, #2214

[jmoore]

(In [7207]) OmeroCli: Updating config on startup and maintaining lock. See #800, #2213, #2214

[jmoore]

(In [7208]) OmeroCli: Adding bin/omero config lock and LockException handling. See #800, #2213, #2214

[jmoore]

(In [7217]) OmeroCli: Upgrade logic for 4.2 configuration properties. See #800, Fix #2213, #2214

[jmoore]

(In [7230]) Removing all access to java.util.prefs.Preferences from server. See #2214, #2491

[jmoore]

(In [7232]) Fixing split on = of old properties. See #2214

[jmoore]

(In [7237]) Changing when etc/grid/config.xml gets created. See #2214

Previously, when bin/omero config could not find etc/grid/config.xml
it loudly fell back to useing ~/omero/config.xml. The first invocation
of bin/omero admin {start,deploy} could then detect the missing config.xml
and run bin/omero config upgrade.

This led to issues where one wanted to configuration before the first
deployment. (Makes sense).

Now, if etc/grid exists, all bin/omero config commands will create
config.xml. A user will need to manually run bin/omero config upgrade
which can be clearly outlined in the upgrade instructions.