Consolidate shared battle loading states

[Paul-Ladyman]

Currently a loading spinner is displayed when waiting for a battle to be shared. There is then a second loading state which displays "..." in the sub title whilst waiting for the player session link to be copied. This state should be removed and the loading spinner displayed until everything is ready or until an error occurs when a suitable error message should be displayed. This will probably require moving the copying of the link up from the sub title component to a higher level where it makes sense to activate the loading screen.

[Paul-Ladyman]

This will also resolve #450