Extracted Authentication to AuthenticationService

[r4inee]

This closes #95, closes #74, closes #63, closes #62, closes #61, closes #5, closes #65, closes #35, Closes #82

• Refactored github authentication from authentication.ts to AuthenticationService
• Edited HTML components and redesigned login/logout process

There still work to be done on #86 as some functionality relies on other services being added. Likely to conflict with #83 @bowenzheng98 Tests are not written yet as this aims to be a template for those who are writing services and tests will be added shortly.

Any comments will be appreciated as this is quite a large change 😄can anyone on windows also try to build it and run it.

edit: UI + Authentication changes Top left corner now shows the username of the user currently signed in.

Clicking on the username shown above will take you to back to the login screen with the option to logout.

Continue without sign in remains the same but have removed the late sign-in option (the old drop down in the header). Sign in button at the top right will redirect back to sign in panel.

If remember login is not checked, then fields are not cleared once user has logged in.

[qw]

Also closes #65. I have edited the main description.

[r4inee]

Closes #35.