The entire page is draggable, except:

- buttons
- any input type
- the filmstrip
- the chat panel

The spinner will be visible until jitsi-meet iframe is completely loaded.

The configured server URL will be used when the room URL is not
a full URL. If a full URL is given, the target server is joined.

The default server URL is https://meet.jit.si

Use the concept of a "server URL", since it's URLs we are dealing with,
not actul domains.

Fixes: #65 

The term "action" is quite overloaded since we use redux,
so let's call it "button" since that's how it behaves.