Better error handling

Right now it's not clear why timelines don't load, you aren't able to login, etc so now a clearer message is shown:

On the timeline

On the login page

Tasks left todo

• Rebase after proxy settings are merged, so it's possible to actually configure them.
• When fixing proxy settings, the accounts aren't properly reloaded and you have to restart anyway.
• Fix the padding of the inline message on the timeline