When adding a new week, allow adding multiple by asking how many weeks to add.

[ChristopherFritz]

When adding a new week, ask for how many weeks to add.

If there are existing weeks, default to 1.

If there are no existing weeks, check if there are any chapters. If so, default to the number of chapters.

If there are no chapters, check if there is an existing prior volume. If so, default to the number of chapters from the prior volume. (Some manga are consistent in number chapters across volumes, and others are not.)