Add option for Operators to send their own invitations

[mikron-ia]

Currently, the only way to invite a player to your Epic when you are an operator is to contact the administrator - which has to be done outside the system.

Add an option to send an invitation to Epic to someone. The system should act differently depending on whether they have an account or not:

• User has no account: send them an invitation with information that they are invited to an Epic and have to create an account to join; link leads to invitation page
• User has an account: send them an information that they have been invited; link leads to the dashboard or invitation / message page