Add shareable repo-specific URL

[nknguyenhc]

Is your feature request related to a problem? Please describe.
Currently, whenever the user wants to view a repo, user has to login, and then indicate the repo. There is no repo-specific URL that user can share with others. Furthermore, after authentication, the app does not redirect to the pathname initially indicated (if any)

Describe the solution you'd like
There are 2 parts to this issue:

1. Add repo-specific URL.

This means that a URL in our repo should indicate which repo the intended landing page will be viewing. For example, https://catcher-org.github.io/WATcher/issueViewer?repo=CATcher-org/WATcher indicates that the intended landing page will be viewing this repo.

2. Redirect to the intended-landing page.

This means that if the user put https://catcher-org.github.io/WATcher/issueViewer?repo=CATcher-org/WATcher to the URL bar in the browser, after authentication, our app should redirect to view the exact same page (i.e. to view this repo), instead of asking from user for which repo to view.

Describe alternatives you've considered
As described below.

Additional context
This is to improve user experience, especially first-time user, as discussed in #236. We should try to simplify the process of logging in and viewing a repo for users. Bypassing logging in was considered, however, due to Github's limitation of 60 requests/hr for REST API endpoints and limitation of GraphQL API endpoints to only authenticated user, it was not very feasible.