Cleanup of the settingsmanager

Added getSettingsWidget on the sublink.
Removed code that checked if it was a sublink in the settings manager
Added defaults and settings widget to the graph

This enables the user to configure default options in the graph that
can be overridden in the node or link configuration.

TODO: Add export of default configuration.
Added the concept of default (global) settings in the configuration.

Please note this commit also includes a fix so that sublinks are
drawn in the correct order. So that if sublinks are drawn in the same
order that they are added in the configuration file.