Developers guide: config chapters not updated to Karaf.

Examples of missing updates:

• "configuration/config.ini" is no more, similar content is now at "etc/custom.properties"
• "Manually create the config file, and put it in the initial configuration folder." does not add custom initial configuration anymore, as XMLDirectoryStorage is not on by default on Karaf. On the other hand, editing existing files in "etc/opendaylight/karaf" does make change indeed, at least when corresponding feature is installed.
• The new default "config-persister-feature-adapter" is not mentioned at all.

Related notes:

• Deprecated paths (such as "configuration/initial") are present throughout both Developers Guide and User Guide.
• It would be nice to include a subchapter on how to edit controller configuration using restconf (instead of netconf client).