Fixes part of #1344: Submit button active/deactive

[rt4914]

Explanation

Fixes part of #1344

The Submit button in Exploration player should be correctly controlled for active/deactive state.

This PR mainly controls the Submit button state under various conditions and renames a file accordingly.

Note: The StateFragmentTest passes on Espresso only and not on Roboelectric. This will be fixed as a part of #973

As a reviewer, you should focus on following manual test cases inPrototype Exploration in First Topic:

1. The Submit button should be inactive by default.
2. In all EditText related input interaction, if there is no text available, the submit button should be disabled.
3. In all EditText related input interaction, if there is error, the submit button should be disabled.
4. In ItemSelectionInteraction, if there is atleast 1 item selected, the submit button should be active.
5. If the learner enters an incorrect answer, clicks submit then after that the submit button should be disabled.

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.

[veena14cs]

Looks great. LGTM.