Change added as a speaker email

[mariobehling]

The email that speakers receive have the "you've been added as a speaker"

In the submission.py change the existing email to the new version below.

        """Hi!

You have been set as the speaker of a proposal to the Call for Participation
of {event}, titled “{title}”. An account has been created for you – please follow
this link to set your account password.

{invitation_link}

Afterwards, you can edit your user profile and see the state of your proposal.

The {event} orga crew"""

Subject: Welcome as a Speaker at {event}!

Hello,

We are excited to inform you that you have been selected as a speaker for {event} with your proposal titled "{title}". To get started, an account has been created for you. Please follow the link below to set your account password:

{invitation_link}

Once you have set your password, you can log in to edit your user profile and track the status of your proposal.

We look forward to your participation and contribution to {event}.

Best regards,
The {event} Organizing Team