Feature: UI/UX Polishing for Classroom

**This issue will be updated continuously with UI/UX improvement tasks.**

### 1. Lack of Teacher onboarding instructions

Currently, the home page doesn't explain how to use the app. The landing page should guide the user on how to use the app, create a classroom, connect students to it, etc.

### (PR #612) 2. Redesign "Create Class" and "Edit Class" modals.

Here are some issues with them:
- The certifications dropdown is too small, and it's not very easy to search through.
- The Edit Class modal does not fully cover the page.
- When editing a Class description, you only have the option to completely replace/rewrite it.
- There is currently a bug where classrooms with no certifications can be created. (#552 handles this, needs to be updated and merged in)

### (PR #610) 3. Redesign Class cards in the Classes page.

Issues:
- Classroom titles and descriptions should wrap or cut off properly, since there isn't a text limit to those fields.
- Add a character limit to the title and description fields.
- From the Classes page, it's difficult to see which certifications are in which class. We should add a tooltip on the side that shows the user which certifications are part of that class.

### 4. Classroom page Improvements

The Classroom page doesn't display information about that classroom, such as the name, description, certification list, etc. We should look into how apps like Google Classroom, Canvas, Schoolloop, handle their teacher dashboards for reference.