Add "Remeber me" option to Login

[adewes]

Currently, the access token is stored in the browser's session storage. Therefore, when closing the browser window, the data will be erased and the when the user opens the app again he/she will have to log in again.

We should add a remember me checkbox to the login dialog. When checked, this should cause the access token to be store in the local storage instead of the session storage, which will make it persistent until the user explicitly logs out.

The accessToken function of the Utils library should automatically check for the access token both in the local storage and the session storage, and should make sure to clear it out from both when logging out the user.