Issue title: Hints after a correct answer reset points
 Issue body: Branch: Nalanda-RCT1

Expected Behavior: On doing some exercise every question accompanied with it's specific hint .When you answered that question hints should be provided when you answered wrong unless that hint is not playing any role in evaluation.
![screenshot from 2014-04-02 18 43 58](https://cloud.githubusercontent.com/assets/6395045/2591203/bae844b0-ba68-11e3-8409-f0758722da90.png)

![screenshot from 2014-04-02 17 38 41](https://cloud.githubusercontent.com/assets/6395045/2591257/872afde2-ba69-11e3-851b-ff3b1cb99427.png)

Current Behavior: Hint is shown even if student answered correctly. If they click on hint even if answered correctly does it reduce its performance report.

![screenshot from 2014-04-02 17 37 06](https://cloud.githubusercontent.com/assets/6395045/2591263/9126c722-ba69-11e3-8040-3911fb3b970b.png)

Steps to reproduce:
1. Login as student 
2. Try to do exercise

 Comments: 
 Comment 0: @him-28 Is the issue that hints are not shown after incorrect answer automatically, or that hints after a correct answer reset points?

 Comment 1: @bcipolli hints after a correct answer reset points

 Comment 2: OK.  Please update the title and text to be clearer on this point.  `Irrelevant to provide hint when the answer is correct.` doesn't indicate that issue well.

 Comment 3: I agree this is something we'd like to do.  However, lower priority given the tight RCT deadline.

Let's do RCT 3, puntable to Nice to Have.

 Comment 4: I will check but I didn't think that looking at hints after a correct
answer reset my points. (I will check again)  I would hope that over time,
alternate solutions will be incorporated into some exercises making looking
at hints after a correct answer, a preferred action.  KEEP ROCKIN' IT.

On Sat, Apr 5, 2014 at 10:46 AM, Ben Cipollini tina27@example.net:

> I agree this is something we'd like to do. However, lower priority given
> the tight RCT deadline.
> 
> Let's do RCT 3, puntable to Nice to Have.
> 
> ## 
> 
> Reply to this email directly or view it on GitHubhttps://github.com/learningequality/ka-lite/issues/1855#issuecomment-39641849
> .

 Comment 5: Fixed in `nalanda-rct2`, with the newest mastery model.

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