Implement proper error handling mechanism

Implement an easy to use error handling mechanism.

Should support displaying snackbars and dialogs. Check the [design in Figma](https://www.figma.com/file/d6n3MPVRWbL5jP2NmvW96b/De_Urgenta?node-id=1466%3A530) for hints on how to design them, but follow the android material design guidelines for them.

These should be displayed easily in case of validation or api errors.

Redirect to login in case auth errors are received from the api. The rest of the api errors should be displayed in a dialog. TBD: api error format

Also, for certain requests, a snackbar error should be shown in case the user attempts to make the api call but is not connected to the internet.

Start by reviewing the linked Figma design and Android Material Design guidance. Then map where validation, API, authentication, and connectivity errors enter the app, including the still-undecided API error format. Done means errors can consistently show dialogs or snackbars, redirect authentication failures to login, and handle offline requests.

Written by the indexing model from the issue text.