Support Multiuser & Epic overlay in the Stormancer EOS plugin for Unreal

[jmderuty]

In order to support overlays, an EOS platform must be created on module startup, then the plugin must be able to use this platform for the first user, and add other platforms in runtime for additional users if necessary (running several users in PIE)

• Create an initial platform used for the overlay on Module startup
• Provide a service to add new users as required on PIE startup.
• Track currently logged in users.
• Log out users on PIE instance shutdown.
• Provide configuration to setup a list of local Dev username which can be used during PIE.

[Falanwe]

Epic overlay is now available when the game has logged in to EOS