Fix #1587: Made intent/bundle/saved/tags instance keys consistent.

[janewaitara]

Explanation

"Fixes oppia#1587: Makes intent/bundle/saved/tags instance keys consistent.

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.

[janewaitara]

@rt4914 PTAL

[rt4914]

@janewaitara This PR has been created incorrectly.
By mistake you have created this PR on your personal fork and not on oppia/oppia-android .

To fix this please follow instructions mentioned in this link at each step:

https://github.com/oppia/oppia-android/wiki#instructions-for-making-a-code-change