Bug fix for GH-71250

Here is a bug fix for GH-71250: `[views of a function] localised decimal mark not recognised`

I saw this bug listed on the Trello board and decided to take a crack at it.

I tested the fix against the following problem seeds:

- http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/views_of_a_function.html?debug&problem=equation-to-table&seed=115
- http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/views_of_a_function.html?debug&problem=table-to-graph&seed=108

Seed 108 is there problem type where you drag the points on the graph based on table coordinates.

For Seed 115, I tested the `equation-to-table` problem type using the following test cases.

__Case 1: Expect correct (passed)__
x = 2,0 and y = 5,0
x = 4.0 and y = 5.0
x = 6 and y = 1
x = 8 and y = -7,0
x = 4.5 and y = 4.375

__Case 2: Expect correct (passed)__
x = 2,0 and y = 5,0
x = 4.0 and y = 5.0
x = 6 and y = 1
x = 8 and y = -7,0
x = 4,5 and y = 4,375

__Case 3 (Mixed decimal/comma x y pairs): Expect correct (passed)__
x = 2,0 and y = 5,0
x = 4.0 and y = 5.0
x = 6 and y = 1
x = 8 and y = -7,0
x = 4.5 and y = 4,375

__Case 4 (Less than 5 points given): Expect wrong (passed)__
x = 2,0 and y = 5,0
x = 4.0 and y = 5.0
x = 6 and y = 1
x = 4,5 and y = 4,375

__Case 5 (Duplicate points): Expect wrong (passed)__
x = 2,0 and y = 5,0
x = 4.0 and y = 5.0
x = 6 and y = 1
x = 4.5 and y = 4.375
x = 4.0 and y = 5.0

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Not the best implementation, but it was the simplest I could I think of.

Trouble that I ran into:

- I ended up adding a `point` form to the `forms` object. The point form accepts an array pair of points `[x,y]`. I could not figure out how to validate values that depended on another. 
- I was not sure how to add the `point` form without adding it directly to the private forms object. Hope that's ok.
- The problem required a minimum of five points, but I could not figure out how to validate the set of points as a whole. I ended up validating each pair individually.