ALTAPPS-1303: Shared, Android mobile content trial

[XanderZhu]

YouTrack Issues:
ALTAPPS-1303

Checklist

Before Code Review:

• Fields "Assignees, Labels, Milestone" are filled in the pull request;
• All checks have been passed;
• Changes have been checked locally.

Description

• Add new MOBILE_CONTENT_TRIAL subscription type & SubscriptionLimitType param to distinct problems & topics limits;
• Mark locked activities & show paywall in study plan, when all free topics are done (see StepCompletionWidgetFeature);
• Show paywall on last available topic completion (see StepCompletionFeature);
• Hide limits for users with MOBILE_CONTENT_TRIAL subscription (see StepQuizFeature, StepQuizToolbarFeature, TopicCompletedModalFeature);
• Consider users without payment ability as Freemium users;
• Update Paywall ui: update strings, replace ContinueWithLimitsClicked action with CloseClicked action.