Added non-reduced fractions option to number-line

Summary:
The number-line can now use non-reduced fractions by calculating the LCM of the denominators
and using that as a base. Fixes T2715.

Test Plan:
- Run Perseus.
- Try some number-line examples [here](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20number-line%201%5D%5D%5Cn%5Cn%5B%5B%E2%98%83%20number-line%202%5D%5D%5Cn%5Cn%5B%5B%E2%98%83%20number-line%203%5D%5D%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22number-line%201%22%3A%7B%22type%22%3A%22number-line%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22range%22%3A%5B0%2C1%5D%2C%22labelRange%22%3A%5Bnull%2C1%5D%2C%22divisionRange%22%3A%5B1%2C10%5D%2C%22labelStyle%22%3A%22non-reduced%22%2C%22labelTicks%22%3Atrue%2C%22numDivisions%22%3A4%2C%22tickStep%22%3Anull%2C%22snapDivisions%22%3A1%2C%22correctRel%22%3A%22eq%22%2C%22correctX%22%3Anull%2C%22initialX%22%3Anull%2C%22base%22%3A1%7D%7D%2C%22number-line%202%22%3A%7B%22type%22%3A%22number-line%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22range%22%3A%5B-1%2C1%5D%2C%22labelStyle%22%3A%22non-reduced%22%2C%22tickStep%22%3Anull%2C%22divisionRange%22%3A%5B1%2C10%5D%2C%22numDivisions%22%3A6%2C%22labelRange%22%3A%5Bnull%2C1%5D%2C%22labelTicks%22%3Atrue%2C%22snapDivisions%22%3A2%2C%22correctRel%22%3A%22eq%22%2C%22correctX%22%3Anull%2C%22initialX%22%3Anull%2C%22base%22%3A1%7D%7D%2C%22number-line%203%22%3A%7B%22type%22%3A%22number-line%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22labelStyle%22%3A%22non-reduced%22%2C%22tickStep%22%3Anull%2C%22divisionRange%22%3A%5B1%2C50%5D%2C%22numDivisions%22%3A4%2C%22range%22%3A%5B0%2C1%5D%2C%22labelRange%22%3A%5Bnull%2C0.625%5D%2C%22labelTicks%22%3Atrue%2C%22snapDivisions%22%3A2%2C%22correctRel%22%3A%22eq%22%2C%22correctX%22%3Anull%2C%22initialX%22%3Anull%2C%22base%22%3A1%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22hints%22%3A%5B%5D%7D). Note that adjusting the 'label' position can also affect the base calculation, as seen in the third example on that page.

Reviewers: jack

Reviewed By: jack

Subscribers: eater

Maniphest Tasks: T2715

Differential Revision: http://phabricator.khanacademy.org/D10068