Assorted UI updates

[Annie-LiGHT]

As part of her semester project report on the DISCO frontend, @gozgun suggested a list of future work. Copied here for future reference. GunesOzgun_DISCOFrontend_Sem2022a.pdf

• [x] Offering dark mode as a theme
• [ ] Adding a progress bar to the Task Creation Form page and updating the button style
• [ ] Adding a tutorial video in Information-Tutorial page to illustrate the steps
• [ ] Include the active page name in the page tab to help users see the open pages
• [x] Including a short explanation for train locally and train collaboratively for Train Your Model step in Tasks page
• [ ] Display the number of models trained in Home page to show impact (e.g. "100 models were trained securely with DISCO")
• [ ] Include the name of the organizations that have worked with DISCO to build trust
• [ ] Create an organized documentation for users and developers on Read the Docs website
• [ ] Create a mailing list to send the recent updates to users
• [x] Create a feedback survey on the website to gather data on experience
• [ ] Require users to have free accounts to create and train tasks to allow them to share their models with other users and secure their models with 2FA