frontend: Snackbars are over the mission buttons on 'flight mode'/'map view'

### Current behaviour

Snackbars cover the mission action buttons on the map view. User has to wait 3s for it to auto-close and sometimes another one opens over it.


### Expected or desired behaviour

Suggested solutions:

* Relocate mission buttons to a cluster (can also be movable by the user);
or
* Relocate the snackbars to the top-center of the screen, right below the Alerter
or
* Integrate snackbars with Alerter, adding colors/'severity levels' to it (Big task with important modifications to the system).
and/or
* Add a close button to every snackbar;

### Prerequisites

- [X] I have checked to make sure that a similar request has not already been filed or fixed.

Start by reproducing the overlap between snackbars and the mission action buttons in the map view, including flight mode and map view. Read the snackbar and Alerter UI entry points, then choose and document one interaction or layout approach; done means snackbars no longer obscure mission buttons and users can access those actions without waiting for auto-close.

Written by the indexing model from the issue text.