[Refactor] Replace "submit" button by "continue"

[spfmoby]

When editing an interval, the "submit" button on the first page suggests that the edition is over and that there is no way to edit the interval duration, warm-up and break times... A simple solution could be to rename the button. An even better solution would be to put everything on the same page, with the same UI (the first and second page have a different UI, the second page on is much more readable/clear/concise.