feature: Improve Button Usability and Consistency in Application

[uddisharma]

Issue 1: Lack of Loading Spinner or Disabled State on Buttons

Description: Buttons in various parts of the application, including the sign-up/login page and video rendering pages, did not have a loading spinner or disabled state. This could lead to users repeatedly clicking buttons while waiting for backend API responses.

Solution: Added loading spinner and disabled state to buttons to prevent multiple clicks and provide visual feedback to users during API calls.

Affected Buttons: Sign-up/Login Page: Signin Button, Video Rendering Page: Mark as Complete Button, Add Comment Button, Upvote Button, Downvote Button Home page : Refresh Database Button

Issue 2: Inconsistency in Button Styles

Description: The buttons for "Mark as Complete" and "Slides" on the video rendering pages were different from other buttons used in the application, leading to inconsistency in button styles.

Solution: Standardized the button styles for "Mark as Complete" and "Slides" to match the rest of the application's buttons for a consistent user experience.