Login button should have a submit and submitted state

[kenlimmj]

Current behaviour:

After entering the username/password and clicking login, the button appears to freeze in the active state while the login is being processed. On a slow connection, this leaves the user wondering if the login is indeed being processed (because there's no indicator otherwise) and if he/she should click the button again.

Proposed behaviour:

On clicking "login", the button state is disabled and the button value is switched to "Logging In". The error "Wrong username/password combination. Try again" should be an active dialog box (i.e. it freezes the rest of the window until it's closed) since it's an important alert and not just a progress update. Once the user has successfully logged in, the login button should be disabled to prevent accidental clicking resulting in a re-send of credentials.