This is plugin for Unreal Editor, creating menu for Avalon tools to run.
This is basically workaround - Unreal cannot create main menu through its Python and the only way I found so far is by using Unreal Editor plugin to do this job and then call functions in python to do the real work.
Plugin is creating basic menu items in Window/Avalon section of Unreal Editor main menu. Clicking on those menu items is calling callbacks that are declared in c++ but needs to be implemented during Unreal Editor startup in Plugins/Avalon/Content/Python/init_unreal.py - this should be executed by Unreal Editor automatically.