Spawn Tacticalmap on overmap

[snipercup]

Fixes #285

Very basic implementation. It picks a random map from /mods/tacticalmaps/ and puts it on the overmap.

• It puts 10 random tacticalmaps on each overmapgrid at a random positoin
• Tactialmaps can't cross the overmapgrid boundaries
• Tacticalmaps can't overlap with eachother
• It will attempt 100 times to place a tacticalmap before hitting it's limit. Usually it finds a position on the first try

I tested that the rockyhill map loads correctly. Here you can see the rockyhill and town_00 on the overmap: