Add Button to Post Anonymously in Post Creation Options

[anna-mat]

Button will give students an option to choose whether their question will be showed to the whole class or anonymous

Estimated effort for each task: Medium
Dependencies among tasks: #15
Milestones to indicate which sprint the issue should be completed in (Sprint 1, Sprint 2, Stretch): Sprint 1
Acceptance criteria that describes how you know this task is done: Test on sample user group of students to ensure they can create an account, create a post and successfully see and click the button