change to simplify translation & limit incoherences (for translations)

[mplusb]

With this link (https://translate.wordpress.org/projects/wp-plugins/rsvp/stable/fr/default/?filters%5Bstatus%5D=untranslated), you can see there are still 6 untranslated messages.

Each one corresponds to the help text displayed below a text input in the settings page of your plugin. Each follows the pattern I described, their goal being showing the actual default value for the text input if not overwritten by the user.

My suggestion would be to split these strings in 2, having just a generic "Default is: " one, and re-using the actual default question string (eg: "If you have any food allergies, please indicate what they are in the "notes" section below. Or, if you just want to send us a note, please feel free. If you have any questions, please send us an email.")

This way, if in the future, you were to change the default value for one question (eg: the one for the comment box I've put previously on food allergies), the change in this default value will automatically be reflected in the settings page without you needing to go & update the actual "Default is: If you have any food allergies, please indicate what they are in the "notes" section below. Or, if you just want to send us a note, please feel free. If you have any questions, please send us an email." too.

Concretely, I would update:
- wp-rsvp.php#L308: <span class="description"><?php _e( 'Default is: "We have the option of getting cheese pizza for the kids (and only kids). Do you want pizza instead of \'adult food?\'"', 'rsvp-plugin' ); ?></span>

to: <span class="description"><?php _e( 'Default is: ', 'rsvp-plugin' ) . '"' . __( 'We have the option of getting cheese pizza for the kids (and only kids). Do you want pizza instead of "adult food?"', 'rsvp-plugin' ) . '"'; ?></span>

Screenshot with the strings in question:
https://gyazo.com/9d2f6406e5dc2034cbbf2fe3096e56d6

https://secure.helpscout.net/conversation/1346510698/33061?folderId=3558549