Make the use of the "study" tab clear

[seanlip]

Platform
Oppia Android

Describe the request

Learners have reported that they find it hard to understand the differences between the two tabs in the topic screen in the Android app -- see #74. We have addressed this partially by changing the tab names to "Learn" and "Study", and, accordingly, that issue has been closed.

However, we might want to revisit some of the other suggestions that arose there, and decide whether to pursue them or not:

• Have a pop up notification on top of the lesson tab to indicate the student should “tap to start learning”.
• Combine learn/study into one section, facilitating quick access for students. For example, study guides could be tasks that come just after each chapter, allowing students to easily identify and engage with them before moving on to the next chapter.
• Make the icons clearer -- check if they're recognizable to younger users. The icons used should be universal and easy to understand at a glance, even without text. Younger learners may not take time to read the labels.

UXR Success criteria

• Learners should consider what is in the current Study tab as an alternative shorter way / reference to learn the material, rather than a set of practice questions or an inadequate summary (where "inadequate" here means that they think it won't be enough without the story-based lessons).
• The learner should be able to clearly articulate the difference between the Lesson and Study tabs.

Context for the request
Please provide enough context for the request. For example:

• Is this a new or existing feature?
• What is the broader user journey that this feature fits into?
• What is the current user experience like (where is the user located before they encounter this feature)? Feel free to add screenshots.

Link to PRD
Please link to the PRD here.

UXR success criteria
For revisions of existing features, list the success criteria for the design here (i.e. what must the design achieve during UXR for it to be considered successful)? E.g. "When a user visits the topic page, they should be able to select their first lesson without needing further prompting."

DESIGN APPROVAL CHECKLIST -- DO NOT EDIT.

• UX Design approved (Android mocks should include dark mode)
• UX Writing approved
• Product approved

For a design project to be completed, it needs approval from UXD, UXW and PM. Please tag the following reviewers when your project is ready (at least one reviewer for each of the bullet points below):

• UXD: @rflore / @S4v8n (for Web projects), @seanlip (for Android projects)
• UXW: @tamiorendain
• PM: @seanlip