Change incompatible exercises; allow for data-weight="0"

- Changed all exercises with `data-weight` equal to some decimal.
- Deleted some exercises with `data-weight=“0”`
- Some exercises with `data-weight=“0”` used it as a template to reduce
redundancy. Since this is clever, I added the one line neccessary to
allow it.
- Deleted (inferior) alternative method that was commented out
- Included `id = $(problem).attr(“id”)` which was an oversight to not
be included the first time around.
- Changed `else if` to `else` because there should be no cases where
`typeof exerciseId === undefined` or `problems.length === 0`.