added grade screen

[rashiranjan22]

Description

I have added a gradescreen Due to absence of a sidebar right now , I added the button to view grades in homescreen I had directly added data for subjects in firestore ,because add/delete logic for the subjects has not been made yet

Related Issue

Fixes #10

Type of Change

• [ ] Bug fix
• [X] New feature
• [ ] Documentation update

Screenshots (if any):

db addition example gradescreen button at homescreen

Checklist

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings

[rashiranjan22]

@Varun-Kolanu , please check

[Varun-Kolanu]

Nicee working pretty well 🌟