Add login functionality on the frontend

[lanterno]

Currently a login button and page exist, but it's not working. the API on the backend is ready, so we need to implement this on the frontend.

• Once a user is logged-in, they should be able to see their username on the website
• The login page should make sure to tell the users that is this page is for authorized users only and not any one can create a user.

Logged-in users should see:

• A link on the manuscript page to edit the manuscript on the admin site
• A link on the image page to edit the image on the admin site
• A link on other pages as well (Where ever it makes sense)

Important

-[ ] Only logged-in users can create annotations on the images. Normal users can only view.