feat: Import status, readings & date added from bookwyrm

[lucalbus]

In the bookwyrm import, fetch reading dates (start date, finish date, stopped date), book status (based on shelf or reading dates) and the date the book has been added to one's book list

[RomanKovtyukh]

I had a concern about writing incomplete Reading to the DB, but apparently it's allowed and done in the past:

openreads/lib/ui/book_screen/book_screen.dart

Lines 84 to 109 in e54ad37

	// finishing the book
	if (status == BookStatus.inProgress) {
	final rating = await _getQuickRating(context);
	book = book.copyWith(
	status: BookStatus.read,
	rating: rating,
	readings: book.readings.isNotEmpty
	? (book.readings..[0] = book.readings[0].copyWith(finishDate: date))
	: [Reading(finishDate: date)],
	);
	} else if (status == BookStatus.forLater) {
	book = book.copyWith(
	status: BookStatus.inProgress,
	readings: book.readings.isNotEmpty
	? (book.readings..[0] = book.readings[0].copyWith(startDate: date))
	: [Reading(startDate: date)],
	);
	} else if (status == BookStatus.unfinished) {
	book = book.copyWith(
	status: BookStatus.inProgress,
	readings: book.readings.isNotEmpty
	? (book.readings..[0] = book.readings[0].copyWith(startDate: date))
	: [Reading(startDate: date)],
	);
	}

[RomanKovtyukh]

Looks good to me