Special spot generation

[bojidar-bg]

Some spots need to be marked as special, e.g.

• Spots next to a planet should be marked as "colony spots"
• Spots next to a trade station should be marked as "trade spots" ( @fry- ~ correct? )

[fry-]

@bojidar-bg correct :)
Colony spots are already existent in the code. stored in the board.gd -> colony_cell array. the trade stations are not implemented yet. also, the code contains some "bugs" since planets on the border of the board are not fully functional yet.

[bojidar-bg]

Mostly done, now waiting for trade stations. (8effd46517846fc364ace617c543833e62b341ff)