[VisionGlass] Update phone UI according to connection state

[felipeerias]

This PR introduces a ModelView instance which can keep track of the connection state, so that the UI will be updated automatically.

The connection states are:

• DISCONNECTED: the VisionGlass is not plugged to the phone
• CONNECTING: the glasses are plugged and set up has started
• REQUESTING_PERMISSIONS: Wolvic is waiting for the user to grant the required USB permission
• CONNECTED: permissions have been granted and the app is setting up the graphics system
• ACTIVE: everything is ready and the user can use Wolvic
• PERMISSIONS_UNAVAILABLE: error state, the user failed to grant the required permission
• DISPLAY_UNAVAILABLE: error state, the initialization of the graphics system has failed

[felipeerias]

Built on top of https://github.com/Igalia/wolvic/pull/1281

[svillar]

I had other issues. Don't remember the exact steps but after starting Wolvic and then connecting the glasses I got the system dialogs and accepted them both. Them I got not one but two Wolvic dialogs reporting errors and then the Wolvic phone UI.

We should be careful because there are tons of potential combinations that the current code takes into account. We should not regress that.

[felipeerias]

@svillar I have updated the PR. Here's a short summary of the changes:

• adjusted the UI state transitions
• reset the internal state when the user disconnects the glasses
• after we switch to 3D mode, the system often removes the current display and adds a different one; we used to display an alert in this case but I have removed it
• changing the value of mPresentationDisplay and mActivePresentation happens at the same time in the showPresentation() method
• add a message in the UI when there is an error, instructing the user to try again
• a few other changes, usually having to do with state transitions or different events