Fix part of #1460: Json file updates for questions and skills

[rt4914]

Explanation

This PR fixes part of #1460

Checklist

• All questions are shifted to a single questions.json file.
• All questions are shifted to a single skills.json file.

Pending

• Structure of question json files needs to be updated. (Will be done in future PR)
• Topic Size Calculation.

How to test:

1. All tests are passing without major change makes sure that the content is parsing correctly.
2. Run the app, go to Fractions-> Practice, start questions.
3. Make ConceptCardFragmentTestActivity as launcher activity and check that it works.

Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• The PR explanation includes the words "Fixes #bugnum: ..." (or "Fixes part of #bugnum" if the PR only partially fixes an issue).
• The PR follows the style guide.
• The PR does not contain any unnecessary auto-generated code from Android Studio.
• The PR is made from a branch that's not called "develop".
• The PR is made from a branch that is up-to-date with "develop".
• The PR's branch is based on "develop" and not on any other branch.
• The PR is assigned to an appropriate reviewer in both the Assignees and the Reviewers sections.

[anandwana001]

LGTM, just some nit changes