More random placement with rmlib2

[elexis]

As discussed with FeXoR in irc yesterday (following #4485), the placeRandom function enforces a 25% map diameter minimum distance between players.

This means if we have 8 players, there will inevitably be one player in the middle and the other players at the edge of the map (at 42% of the map diameter).

(1) The 25% diameter minimum distance is well suited for the tiny mapsize, as it results in an absolute distance of 128 (see map_sizes.json) * 25% = 32 tiles, so that players have sufficient initial territory (and iberian walls won't collide with enemies territory), while yielding more random patterns with 8 players on greater than tiny mapsizes.

(2) These numbers should become arguments of that function with default values (so that maps could pick custom values).

[FeXoR]

If the map size is not tiny or small the center could be avoided like the map border to not get that player in the middle. That also should be an argument so it can be turned off if preferred.