Change Rail Bridge, do to being invisible after destroy

Patch Note:

Reworked Wooden bridge
Removed all four wooden bridges and replace with a island and and two wooden bridge.

Reworked Train bridge
Removed all three Train trestle bridges and replace with a single train trestle bridge.

Add more marsh land on river bank
Made small sandbars and chopped up the river banks to give a more realistic feel.

Add center objective
the Center island now is it own objective, it helps divided the two sides as well as giving the map an other flash point.