Fix #156 & #157: Continue/End Exploration player buttons- low-fi

[rt4914]

Explanation

This fixes #156 and #157 and introduces following buttons which will be used in state:

1. Interaction Button -> Continue, Return to Topic, Submit
2. Previous Arrow Button
3. Next Arrow Button

Some dummy code has been introduced in the PR to make it functional and appropriate TODOs have been added to update them in future PRs.

Also, if Interaction Id is MultipleChoiceInput, then in this PR we are directly showing Submit button and in final implementation, the Submit button should not be displayed until the learner selects an answer. Similarly in TextInput, NumericInput, the Submit button is active but in final implementation it will inactive at first and will only be active if learner has typed some answer in edit-text.

Reference Design Doc: https://docs.google.com/document/d/1iD4sY_hWmWRu4eC8jGoolKQ5hsqpIV5sG1NA4YB2HL4/edit?usp=sharing

This PR was earlier on #185 and #222

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 assigned to an appropriate reviewer.

[rt4914]

@nikitamarysolomanpvt @veena14cs @BenHenning This PR is ready for review.

[veena14cs]

Looks good.

[BenHenning]

Thanks @rt4914. This is an excellent start for state fragment! I'm inclined to approve the changes despite the comments, but I'm happy to discuss individual items further offline or do one more review pass if you'd like.

[rt4914]

@BenHenning All conversations have been resolved and appropriate issues have been filed.

Merging this PR now.