LoginDialog going solo

[sssoleileraaa]

Description

Resolves #286
Note: This does not include any styling

Summary of changes

• When you start the client, instead of showing both the main window and login dialog, we now only show the login dialog
• There's now an option to click on "offline mode" which shows the main window without allowing behavior that requires authentication
• When you log in via the main window 'SIGN IN' button, the login dialog still pops up without hiding the main window
• Exiting the login dialog when it's the only window that shows closes the application

Test

1. Start the client and see login dialog appears without main window
2. Click "offline mode" and main window appears in offline mode
3. Log in using the 'SIGN IN' button and see login dialog popup. Here you can click offline mode again or login.
4. Start the client again and log in with credentials this time.
5. Start the client again and before opening the main window by clicking on sign in or offline mode, close the login dialog and verify that it closes the application.
6. Start the client again and when the main window is open (by either clicking on sign in or offline mode), reopen and exit the login dialog window, and verify that the application continues to run.