Calculate line position for cues with their snapToLines flag set.

- This supports horizontal text only. It needs a few tweaks
to fully support vertical text.
Calculate line position for cues with their snapToLines flag set.

- This supports horizontal text only. It needs a few tweaks
to fully support vertical text.
- The test suite has been altered to balance the computed values on
different platforms for the processing model tests since computed
values will be different.
Finish algorithm to position boxes when their snapToLines flag is not set.