Feature: enable configurable node type "profiles" / presets #751

Based on the discussion in PR #742 :

• user-configurable node type "profiles" / presets could be defined
• then, this node type can be added using "add "
• or added in the GUI by clicking the type's button.
  • (the GUI would need to dynamically add buttons or entries for types that are defined)

The configuration of new profiles could be done in one or more ways:

• load from YAML file (provided as OTNS argument, or loaded runtime using 'load')
• provide as OTNS argument on cmdline
• load from an OTNS script file (i.e. just a linear list of OTNS CLI commands sent) - provided as OTNS argument or loaded runtime
• in the CLI, by a new command related to the 'exe' command

This issue is to collect any preferences/requirements for the feature and discuss design ideas.