Multiplayer concurrent space battle.

```
As we plan to do a many-against-many multiplayer, it requires a constant
real-time mode. Therefore, the current 1-on-1 stop the world type space battle
mechanic won't work, and the SpacewarScreen won't either.

Therefore, I suggest creating a brand-new, tabbed spacewar screen, where
multiple ongoing battles could be observed and managed, but lets the player
enter and exit to do colony management if he/she wishes.

Some considerations:

-remove most panels and have a much simpler layout:
[ space surface ]
[commands][selection][statistics]

- what if a defender adds a space station in middle of the battle?
- what if other fleets of the parties join?
- what if other players join? (this requires non-overlapping at least)
- users leaving their fleet temporarily might enable some AI on their behalf
with a few objectives/parameters
- Modifying the planet screen should be much simpler since less battle related
event depends on it.
- new UI will be required to keep track of ongoing battles when on other
screens.

```

Original issue reported on code.google.com by `akarn...@gmail.com` on 17 Aug 2012 at 9:40