Login to Github before entering repository name (dialog popup)

[chia-yh]

Summary:

Attempt to resolve #154
Alternative to #169 as suggested in #154 (comment)

WATcher allows users to change repositories, i.e., the repository is not fixed like in CATcher. Having users login first, then being able to choose the repository they wish to see would allow for a smoother UX, e.g.

Login -> Sign in to Github -> Confirm Login Account -> Issues Dashboard (Popup to select repository)

Currently displays a minimal login card that redirects users to sign in to Github. Future enhancements to the UI would be desirable.

Type of change:

• ✨ New Feature/ Enhancement

Changes Made:

• Add login.component, which extracts the AuthService::startOAuthProcess() call from session-selection.component.ts that allows users to login to Github
• Add some tests for login.component in login.component.spec.test
• Extract user data setup from ConfirmLoginComponent::completeLoginProcess() to AuthService::setupUserData(), leaving the creation of the user model, after which authentication state is changed to authenticated
• Move handleAuthSuccess() from ConfirmLoginComponent to AuthService
• Modify ConfirmLoginComponent tests as necessary
• Add repoSetSource, repoSetState, isRepoSet() to AuthService
• Change auth.component.html to show LoginComponent instead of SessionSelectionComponent by default
• Change auth.component.html to prevent current session from being shown on the login card for confirming login account, as no session has been set at that point of the process
• initializeRepoNameInTitle() method call in HeaderComponent now subscribes to repoSetState instead of currentAuthState, and checks isAuthenticated() && isRepoSet() before calling the method, html uses isRepoSet() to display buttons requiring a current repository after one has been set
• Subscription to currentAuthState in HeaderComponent now calls openChangeRepoDialog after user is authenticated
• Header, button text, tooltips for RepoChangeFormComponent now differs based on if a repository has already been selected

Screenshots:

Proposed Commit Message:

Change auth process to login before selecting repo

Users select a repository before login.

WATcher does not fix a single repository, and allows users to change the
selected repository.

Having users login to Github prior to selecting a repository would
facilitate a smoother UX.

Let's allow users to login before choosing a repository.

Checklist:

• I have tested my changes thoroughly.
• I have created tests for any new code files created in this PR or provided a link to a issue/PR that addresses this.
• I have added or modified code comments to improve code readability where necessary.
• I have updated the project's documentation as necessary.

[gycgabriel]

Will review this after merging #169 because this builds on that

[gycgabriel]

LGTM