Create a gridID for shield grids with Zero-K's lua gadgets

### Conclusion: ###

I want a gridID for every shield grid in a game like http://Zero-K.info.

BUT

Grids
* can get decimated by a single shield at a time
* can grow by adding new shields
* removed at once or by a random percentage by atomar nukes
* split into a random number of grids
* created from a new shield unit and a random number of grids
* can have only 1 shield


### Numbers and Table-sizes ###

IMPORTANT:
Above the following specifications, lags are possible and caused by boring or Epic_Shore-games.
If you get over these specifications, the rest of the code would lag anyway.

Unit ids:
1 to 500 (extreme cases like chicken games)

Teams:
1-4 (extreme cases like FFA)

Max shields per team:
250 shields *2 teams
125 shields *4 teams

Worst case(s):
190 in the biggest group and 20 single groups with up to 3 entries each (per team)
250 shields in 150 groups


### Code structures ###

Original code source: http://code.google.com/p/zero-k/source/browse/trunk/mods/zk/LuaRules/Gadgets/unit_shield_link.lua

AdjustLinks() is called every Second from gadget:GameFrame


### Table structures ###

shieldUnit = {
    -- shield unit created:
    capacity = max charge
    regen = charge+
    regenEfficiency = charge+ / energy-

    -- AdjustLinks() re-generates every second:
    link = { [unitID] = shieldUnit, ... } --each shieldUnit of a grid has the same table
    x, y, z = unit position
    linkable = not inbuild and not stunned and not active == false and valid unit position

    --[[
        --su = shieldUnit = customTable --every Spring unit which got a shield has one customTable
        --id = UnitID from Spring
        if  su5 connects su(1&2) with su(3&4)
        then  su(1..5).link == { id5=su5, id1=su1, id2=su2, id3=su3, id4=su4 }
    --]]
}

shieldConnections[teamID] = { --created by AdjustLinks()
    [unitID1]=(adjacent unitID2),
    --NEVER [unitID2]=unitID1,
    [unitID3]=(adjacent unitID4),
    ...
}


And lua-tables are not sorted in the order you added the entries if you don't assign values to incremental keys
* It might get out as 3,1,5,2,4